Senate Republicans are demanding the administration hand over all documents related to Jack Lew’s failure, when he was head of the Office of Management and Budget, to comply with a law aimed at ensuring Medicare’s solvency.

The demand, led by Senate Budget Committee ranking member Jeff Sessions (R-Ala.), is the latest sign the GOP may be intent on building a case against Lew, who was tapped by President Obama earlier this month to replace Treasury Secretary Timothy Geithner. Lew has served most recently as Obama’s chief of staff.

Most GOP senators haven’t said how they would vote, but those who have are expressing reservations about Lew, who irritated Republicans during last summer’s debt talks. Sessions has said Lew “must never” be Treasury secretary and has criticized the former top Obama aide for submitting budgets that failed to receive any votes in Congress.