The ECB has increased pressure on Greece by making it more expensive for the country's banks to access cash.
It says it will no longer accept Government bonds as collateral for loans to commercial banks.
The move has prompted fears of a run on Greek lenders as the country struggles to avoid defaulting on its debts.
The European Central Bank's announcement came just hours after Mario Draghi met Greece's new Finance Minister Yannis Varoufakis.
The ECB says it's taken the decision – to withdraw a key borrowing option for Greek banks – because it cannot be certain about a “successful” deal on Greece's 240 billion euro bailout.
In practice, it means banks will find it more expensive to get more cash – and it's led to fears about shortages and runs at lenders.
The move has ratcheted up the pressure on Athens – which is trying to renegotiate the strict conditions of that rescue package.
Prime Minister Tsipras says the decision will have no adverse impact – and claims its sector is fully protected.
Meanwhile, Enda Kenny is in Brussels today, where he'll meet EC President Jean Claude Juncker – there will be pressure on the Taoiseach to secure more debt deals for Ireland.
