(Bloomberg) -- With many of the largest U.S. college endowments at record values, two congressional committees that determine tax policy jointly opened an inquiry about how the wealthiest schools manage and spend those funds.

The Republican leadership of the Senate Finance Committee and the House Ways and Means Committee sent letters late Monday by email to 56 private schools with assets of more than $1 billion, citing their “numerous tax preferences,” and adding weight to the federal scrutiny of college endowments.

Congress is evaluating the value of federal policies that permit tax-free investment earnings for schools and tax deductions for donors.