WASHINGTON (AP) — The White House is promising to veto Republican-backed legislation that would prevent the government from withholding 3 percent of payments to government contractors.

The legislation faces a test vote in the Senate late Thursday. Even though President Barack Obama supports the idea, the White House promised a veto because it would be paid for with $30 billion in cuts from domestic agency spending.

The withholding law was passed in 2005 by a GOP-controlled Congress. The idea then was to make sure contractors couldn't duck their taxes. But the rule has yet to be implemented. Advocates of repealing it say it will help create jobs, especially from contractors with smaller profit margins on large projects.

Senate Democratic leader Harry Reid promised that the withholding requirement would be repealed in coming weeks.