On the heels of a legislative victory this week for small and midsize banks, bigger banks including JPMorgan and Citigroup are lobbying congressional Republicans in an effort to ensure a victory of their own.

Large banks are pushing Congress to redefine swap transactions made between different affiliates of the same company so that they aren’t subject to certain rules stemming from the 2010 Dodd-Frank Act. The move would prevent regulators from forcing banks to post collateral for those transactions, potentially saving banks hundreds of millions of dollars in compliance costs.