The European Central Bank needs fresh powers to freeze payments temporarily at banks heading towards failure, halting a potentially fatal outflow of liquidity, Daniele Nouy, the ECB’s top supervisor said Friday.

The ECB, which supervises the euro zone’s biggest banks, was tested in recent months when several top lenders failed in quick succession, including Spain’s Banco Popular, which collapsed when liquidity dried up in a matter of days.

“In my view… the introduction of adequate moratorium power for authorities is needed in order to react with the needed flexibility, if the situation of a bank deteriorates rapidly,” Nouy told a member of the European Parliament in a letter.

“Given the potentially swift evolution of liquidity crises, a moratorium tool could be necessary to ensure there is adequate time for ensuring a credible solution,” Nouy said, adding that the ECB will soon publish an opinion on this issue.

Countries like Greece or Germany allow for such freezes but not Spain, and ECB wants uniform rules across the euro zone.

Supervisors are also concerned that when a bank is near collapse but not yet legally deemed “failing or likely to fail,” they lack the tool to intervene and prevent the death spiral.

The moratorium tool could maintain some liquidity, allowing authorities to guide the bank either into orderly resolution or a rescue.

The European Commission late last year proposed giving supervisors the authority to suspend some deposit withdrawals and payments obligations in exceptional circumstances.

While the Commission proposal would excluded deposits under 100,000 euros, the Single Resolution Board has warned that significant amounts of cash could leave the bank if the moratorium was excessively narrow.

Lawmakers since the Banco Popular failure have debated whether to include even smaller deposits in the moratorium.