The European Union's decision to postpone collateral rules for swaps is putting pressure on U.S. regulators to follow suit to avoid rupturing the $493 trillion market dominated by the world's biggest banks.

The European Commission, the EU's executive arm, said last week it won't be able to meet a September deadline set by the U.S.—and laid out as goal by global regulators—for standards that seek to ensure banks have sufficient collateral to backstop transactions done directly with other traders. Europe plans to complete the regulations by year-end, though they may not take effect until mid-2017, according to the commission in Brussels.

The timing gap threatens to raise competitive pressures, since U.S. banks will need to comply with the rules starting in September, possibly affecting billions of dollars in collateral. This divergence could discourage trading between U.S. and European banks in the interim and make it more expensive for U.S. banks.