"We request that the Treasury Department delay the implementation of the sanctions termination to allow sufficient time for you to fully brief Members on this matter and to resolve the pending questions," the lawmakers wrote in their letter to Mnuchin.
They also asked that Mnuchin fulfil the request for a delay by Friday, January 11.
Previously, the US Treasury Department's Office of Foreign Asset Control (OFAC) said Rusal, EN+ Group and JSC EuroSibEnergo agreed to undertake restructuring for the sanctions to be lifted.
READ MORE: US Treasury Extends Expiration of Rusal, En+ General Licenses
OFAC Director Andrea Gacki explained that the three companies had agreed to make significant changes that would include reducing Russian businessman Oleg Deripaska's direct and indirect shareholdings in the entities to below 50 percent.