diff --git a/substrate/node/runtime/src/lib.rs b/substrate/node/runtime/src/lib.rs
index 0c1a229ab2..f6955d2bd0 100644
--- a/substrate/node/runtime/src/lib.rs
+++ b/substrate/node/runtime/src/lib.rs
@@ -211,6 +211,9 @@ impl_opaque_keys! {
 // `SessionKeys`.
 // TODO: Introduce some structure to tie these together to make it a bit less of a footgun. This
 // should be easy, since OneSessionHandler trait provides the `Key` as an associated type. #2858
+parameter_types! {
+	pub const DisabledValidatorsThreshold: Perbill = Perbill::from_percent(17);
+}
 
 impl session::Trait for Runtime {
 	type OnSessionEnding = Staking;
@@ -221,6 +224,7 @@ impl session::Trait for Runtime {
 	type ValidatorId = AccountId;
 	type ValidatorIdOf = staking::StashOf<Self>;
 	type SelectInitialValidators = Staking;
+	type DisabledValidatorsThreshold = DisabledValidatorsThreshold;
 }
 
 impl session::historical::Trait for Runtime {
diff --git a/substrate/srml/authority-discovery/src/lib.rs b/substrate/srml/authority-discovery/src/lib.rs
index 372a48cc7f..8032b46be4 100644
--- a/substrate/srml/authority-discovery/src/lib.rs
+++ b/substrate/srml/authority-discovery/src/lib.rs
@@ -155,6 +155,10 @@ mod tests {
 		}
 	}
 
+	parameter_types! {
+		pub const DisabledValidatorsThreshold: Perbill = Perbill::from_percent(33);
+	}
+
 	impl session::Trait for Test {
 		type OnSessionEnding = TestOnSessionEnding;
 		type Keys = UintAuthorityId;
@@ -164,6 +168,7 @@ mod tests {
 		type ValidatorId = AuthorityId;
 		type ValidatorIdOf = ConvertInto;
 		type SelectInitialValidators = ();
+		type DisabledValidatorsThreshold = DisabledValidatorsThreshold;
 	}
 
 	impl session::historical::Trait for Test {
diff --git a/substrate/srml/im-online/src/mock.rs b/substrate/srml/im-online/src/mock.rs
index ba1a7a7d0a..a7b669ddb8 100644
--- a/substrate/srml/im-online/src/mock.rs
+++ b/substrate/srml/im-online/src/mock.rs
@@ -125,6 +125,10 @@ parameter_types! {
 	pub const Offset: u64 = 0;
 }
 
+parameter_types! {
+	pub const DisabledValidatorsThreshold: Perbill = Perbill::from_percent(33);
+}
+
 impl session::Trait for Runtime {
 	type ShouldEndSession = session::PeriodicSessions<Period, Offset>;
 	type OnSessionEnding = session::historical::NoteHistoricalRoot<Runtime, TestOnSessionEnding>;
@@ -134,6 +138,7 @@ impl session::Trait for Runtime {
 	type Keys = UintAuthorityId;
 	type Event = ();
 	type SelectInitialValidators = ();
+	type DisabledValidatorsThreshold = DisabledValidatorsThreshold;
 }
 
 impl session::historical::Trait for Runtime {
diff --git a/substrate/srml/session/src/lib.rs b/substrate/srml/session/src/lib.rs
index 8edb80e8cb..1494f88413 100644
--- a/substrate/srml/session/src/lib.rs
+++ b/substrate/srml/session/src/lib.rs
@@ -121,7 +121,7 @@
 
 use rstd::{prelude::*, marker::PhantomData, ops::{Sub, Rem}};
 use codec::Decode;
-use sr_primitives::{KeyTypeId, RuntimeAppPublic};
+use sr_primitives::{KeyTypeId, Perbill, RuntimeAppPublic};
 use sr_primitives::weights::SimpleDispatchInfo;
 use sr_primitives::traits::{Convert, Zero, Member, OpaqueKeys};
 use sr_staking_primitives::SessionIndex;
@@ -334,6 +334,12 @@ pub trait Trait: system::Trait {
 	/// The keys.
 	type Keys: OpaqueKeys + Member + Parameter + Default;
 
+	/// The fraction of validators set that is safe to be disabled.
+	///
+	/// After the threshold is reached `disabled` method starts to return true,
+	/// which in combination with `srml_staking` forces a new era.
+	type DisabledValidatorsThreshold: Get<Perbill>;
+
 	/// Select initial validators.
 	type SelectInitialValidators: SelectInitialValidators<Self::ValidatorId>;
 }
@@ -356,6 +362,11 @@ decl_storage! {
 		/// will be used to determine the validator's session keys.
 		QueuedKeys get(queued_keys): Vec<(T::ValidatorId, T::Keys)>;
 
+		/// Indices of disabled validators.
+		///
+		/// The set is cleared when `on_session_ending` returns a new set of identities.
+		DisabledValidators get(disabled_validators): Vec<u32>;
+
 		/// The next session keys for a validator.
 		///
 		/// The first key is always `DEDUP_KEY_PREFIX` to have all the data in the same branch of
@@ -475,6 +486,11 @@ impl<T: Trait> Module<T> {
 			.collect::<Vec<_>>();
 		<Validators<T>>::put(&validators);
 
+		if changed {
+			// reset disabled validators
+			DisabledValidators::take();
+		}
+
 		let applied_at = session_index + 2;
 
 		// Get next validator set.
@@ -539,13 +555,36 @@ impl<T: Trait> Module<T> {
 	}
 
 	/// Disable the validator of index `i`.
-	pub fn disable_index(i: usize) {
-		T::SessionHandler::on_disabled(i);
+	///
+	/// Returns `true` if this causes a `DisabledValidatorsThreshold` of validators
+	/// to be already disabled.
+	pub fn disable_index(i: usize) -> bool {
+		let (fire_event, threshold_reached) = DisabledValidators::mutate(|disabled| {
+			let i = i as u32;
+			if let Err(index) = disabled.binary_search(&i) {
+				let count = <Validators<T>>::decode_len().unwrap_or(0) as u32;
+				let threshold = T::DisabledValidatorsThreshold::get() * count;
+				disabled.insert(index, i);
+				(true, disabled.len() as u32 > threshold)
+			} else {
+				(false, false)
+			}
+		});
+
+		if fire_event {
+			T::SessionHandler::on_disabled(i);
+		}
+
+		threshold_reached
 	}
 
-	/// Disable the validator identified by `c`. (If using with the staking module, this would be
-	/// their *stash* account.)
-	pub fn disable(c: &T::ValidatorId) -> rstd::result::Result<(), ()> {
+	/// Disable the validator identified by `c`. (If using with the staking module,
+	/// this would be their *stash* account.)
+	///
+	/// Returns `Ok(true)` if more than `DisabledValidatorsThreshold` validators in current
+	/// session is already disabled.
+	/// If used with the staking module it allows to force a new era in such case.
+	pub fn disable(c: &T::ValidatorId) -> rstd::result::Result<bool, ()> {
 		Self::validators().iter().position(|i| i == c).map(Self::disable_index).ok_or(())
 	}
 
@@ -924,4 +963,22 @@ mod tests {
 			);
 		});
 	}
+
+	#[test]
+	fn return_true_if_more_than_third_is_disabled() {
+		with_externalities(&mut new_test_ext(), || {
+			set_next_validators(vec![1, 2, 3, 4, 5, 6, 7]);
+			force_new_session();
+			initialize_block(1);
+			// apply the new validator set
+			force_new_session();
+			initialize_block(2);
+
+			assert_eq!(Session::disable_index(0), false);
+			assert_eq!(Session::disable_index(1), false);
+			assert_eq!(Session::disable_index(2), true);
+			assert_eq!(Session::disable_index(3), true);
+		});
+
+	}
 }
diff --git a/substrate/srml/session/src/mock.rs b/substrate/srml/session/src/mock.rs
index fe9a4ee936..736d3fa4da 100644
--- a/substrate/srml/session/src/mock.rs
+++ b/substrate/srml/session/src/mock.rs
@@ -183,6 +183,10 @@ impl timestamp::Trait for Test {
 	type MinimumPeriod = MinimumPeriod;
 }
 
+parameter_types! {
+	pub const DisabledValidatorsThreshold: Perbill = Perbill::from_percent(33);
+}
+
 impl Trait for Test {
 	type ShouldEndSession = TestShouldEndSession;
 	#[cfg(feature = "historical")]
@@ -195,6 +199,7 @@ impl Trait for Test {
 	type Keys = MockSessionKeys;
 	type Event = ();
 	type SelectInitialValidators = ();
+	type DisabledValidatorsThreshold = DisabledValidatorsThreshold;
 }
 
 #[cfg(feature = "historical")]
diff --git a/substrate/srml/staking/src/lib.rs b/substrate/srml/staking/src/lib.rs
index 831629f5f2..3f88b67875 100644
--- a/substrate/srml/staking/src/lib.rs
+++ b/substrate/srml/staking/src/lib.rs
@@ -454,7 +454,11 @@ type MomentOf<T>= <<T as Trait>::Time as Time>::Moment;
 /// This is needed because `Staking` sets the `ValidatorIdOf` of the `session::Trait`
 pub trait SessionInterface<AccountId>: system::Trait {
 	/// Disable a given validator by stash ID.
-	fn disable_validator(validator: &AccountId) -> Result<(), ()>;
+	///
+	/// Returns `true` if new era should be forced at the end of this session.
+	/// This allows preventing a situation where there is too many validators
+	/// disabled and block production stalls.
+	fn disable_validator(validator: &AccountId) -> Result<bool, ()>;
 	/// Get the validators from session.
 	fn validators() -> Vec<AccountId>;
 	/// Prune historical session tries up to but not including the given index.
@@ -472,7 +476,7 @@ impl<T: Trait> SessionInterface<<T as system::Trait>::AccountId> for T where
 	T::SelectInitialValidators: session::SelectInitialValidators<<T as system::Trait>::AccountId>,
 	T::ValidatorIdOf: Convert<<T as system::Trait>::AccountId, Option<<T as system::Trait>::AccountId>>
 {
-	fn disable_validator(validator: &<T as system::Trait>::AccountId) -> Result<(), ()> {
+	fn disable_validator(validator: &<T as system::Trait>::AccountId) -> Result<bool, ()> {
 		<session::Module<T>>::disable(validator)
 	}
 
@@ -1531,10 +1535,11 @@ impl <T: Trait> OnOffenceHandler<T::AccountId, session::historical::Identificati
 				continue;
 			}
 
-			// make sure to disable validator in next sessions
-			let _ = T::SessionInterface::disable_validator(stash);
-			// force a new era, to select a new validator set
-			ForceEra::put(Forcing::ForceNew);
+			// make sure to disable validator till the end of this session
+			if T::SessionInterface::disable_validator(stash).unwrap_or(false) {
+				// force a new era, to select a new validator set
+				ForceEra::put(Forcing::ForceNew);
+			}
 			// actually slash the validator
 			let slashed_amount = Self::slash_validator(stash, amount, exposure, &mut journal);
 
diff --git a/substrate/srml/staking/src/mock.rs b/substrate/srml/staking/src/mock.rs
index ace06ed771..747ee64470 100644
--- a/substrate/srml/staking/src/mock.rs
+++ b/substrate/srml/staking/src/mock.rs
@@ -150,6 +150,7 @@ parameter_types! {
 	pub const Period: BlockNumber = 1;
 	pub const Offset: BlockNumber = 0;
 	pub const UncleGenerations: u64 = 0;
+	pub const DisabledValidatorsThreshold: Perbill = Perbill::from_percent(33);
 }
 impl session::Trait for Test {
 	type OnSessionEnding = session::historical::NoteHistoricalRoot<Test, Staking>;
@@ -160,6 +161,7 @@ impl session::Trait for Test {
 	type ValidatorId = AccountId;
 	type ValidatorIdOf = crate::StashOf<Test>;
 	type SelectInitialValidators = Staking;
+	type DisabledValidatorsThreshold = DisabledValidatorsThreshold;
 }
 
 impl session::historical::Trait for Test {