So it is scrambling to find new, even radical ways to fill the shortfall — including a proposal to recruit citizens and tourists to spy on suspected tax evaders.

Greece's coffers may be empty before the end of this month, as tax receipts shrink and the economy shows signs of lapsing back into recession. Athens officials have hinted they may have trouble repaying or refinancing a total of about 7 billion euros, or $7.7 billion, owed in March to the International Monetary Fund and other creditors, or meeting government salary and pension obligations.

Prime Minister Alexis Tsipras has tried to reassure creditors that Greece will not default. But in a sign of how desperately Greece needs money, his government plans on Monday to present a raft of measures to European finance ministers in Brussels in hopes of unlocking aid quickly.