The debt downgrade is raising concerns that investors could reevaluate their appetite for U.S. government bonds, with the potential for rising yields.

The move came as Republicans seek to approve a large package of tax cuts, spending hikes and safety-net reductions which could add trillions of dollars in U.S. debt.

The Treasury plans to auction $16 billion of 20-year bonds, with results due just after 1 p.m. Eastern. The offering will mark the first auction of longer-duration Treasury bonds since Moody’s on Friday became the third and final rating agency to strip the U.S. of its top Triple-A credit rating.