The European Central Bank (ECB) is sending a message to the euro area's leaders: Don't make us pull the trigger on Greece's banks.

After the Frankfurt-based ECB blessed the expansion of so-called Emergency Liquidity Assistance (ELA) to the debt-stricken country's lenders by about 5 billion euros (US$5.7 billion) on Thursday, officials are insisting that continued support is contingent on political talks over Greece's bailout. Greek stocks and bonds rallied Friday, after Prime Minister Alexis Tsipras hinted at progress.

The ECB does not want to be pushed into a position where it is making decisions on the future of the Greek banking system—and the country's membership in the Eurozone—without political cover from European capitals. If talks on a “bridge” financing deal for Greece break down again, ECB President Mario Draghi will have to weigh whether to ration funds further or threaten a veto, just as he did in Cyprus two years ago.