Greece is anxiously awaiting a decision by the European Central Bank on whether to increase the emergency liquidity assistance banks can draw on from the country's central bank.

Worried Greeks on Sunday kept lining up at ATM machines after the prime minister called Saturday for a referendum on creditors' financial proposals in return for rescue loans. Prime Minister Alexis Tsipras' move has startled Greece's European partners and thrown the country's bailout negotiations with international lenders into turmoil.

If the ECB decides Sunday not to increase the emergency liquidity, which currently stands at just under 90 billion euros ($100 billion), Greece's banks will soon run out of cash and restrictions on transactions will likely be imposed.

Parliament approved Tsipras' referendum call early Sunday, with the national vote set for July 5.