European Central Bank policymakers are considering tightening Greek banks’ use of an emergency funding lifeline, but keeping open the backup facility, people familiar with the matter said. Such a move would curb those lenders’ access to a multibillion-euro central bank support mechanism that they use to pay out deposits, making it harder for them to meet such demands.

“There is a possibility of an extension,” said one of the people with direct knowledge of the telephone discussion among the ECB’s decision-making Governing Council, adding that a bigger so-called haircut is being discussed. Such a step involves imposing a higher valuation discount on the security banks offer for this funding to reflect the impact of Greece’s likely default on an International Monetary Fund payment due Tuesday.

If the haircut is steeper in the future than it is at present, it would curbs banks’ use of this Emergency Liquidity Assistance (ELA). But the calculation is not usually publicized, meaning it would not be clear how much such funding had been closed off. The limit for funding is now roughly 89.0 billion euros ($99.4 billion), sources have told Reuters, and it has been held steady at this level for a number of days amid growing protest by Germany.

Even before Greek Prime Minister Alexis Tsipras called a referendum on creditors’ bailout demands for next Sunday, the head of Germany’s Bundesbank had criticized the use of such emergency credit.

If Greece were to leave the eurozone, this funding, which is a form of overdraft with the eurozone’s central-bank system, would fall to the bloc’s other members to pay.

Speaking on German television Saturday, German Finance Minister Wolfgang Schaeuble put a question mark over the solvency of Greek banks, a key condition to qualify to receive such finance. “The ECB has always said that as long as Greek banks are solvent, then emergency loans, the ELA, can be granted,” he said. “And now there is naturally a new situation that, because of the developments, the liquidity and solvency of Greek banks, or some Greek banks, could be in doubt.”

(Reporting by John O’Donnell; additional reporting by Erik Kirschbaum; editing by Jonathan Gould and Jason Neely)