Republicans in the United States Senate were prepared on Wednesday to try to derail Democratic President Joe Biden’s COVID-19 vaccination and testing mandate for private firms, in a legislative campaign that looked to have enough Democratic backing to succeed.

An aide said Republican Senator Mike Braun was likely to go on the Senate floor later in the day to set up a vote under a statute that empowers Congress to override executive decisions.

The proposal, which is expected to clear the Senate but face stiff opposition in the House and a presidential veto threat, would repeal Biden administration guidelines requiring bigger private corporations to mandate vaccines or coronavirus testing for millions of workers.

The measure is not subject to Senate rules that require 60 of the 100 members to agree on most legislation, meaning it could pass with just a 51-vote simple majority. Two Senate Democrats — Joe Manchin and Jon Tester — have voiced support for the bill.

If passed, it would face an uphill battle in the Democratic-controlled House. The White House has also warned that Biden could veto the measure.

The initiative, along with a similar Republican effort that failed in the Senate last week after risking a government shutdown, underscores the intense political opposition facing Biden administration efforts to combat COVID-19, at a time when health officials are trying to contain the highly contagious Omicron variant.

On Tuesday, a U.S. judge in Georgia blocked a Biden vaccine mandate aimed at federal contractors.

The United States has the world’s highest daily average of new coronavirus infections. COVID-19 infected 49.5 million Americans and killed more than 794,000, according to the Reuters COVID-19 Tracker.

The White House said in a statement on Tuesday that employers would face no burden from the mandate because the vast majority of American adults are fully vaccinated and the rule exempts small businesses.