Senate Republicans are filing a formal challenge to President Biden’s vaccinate-or-test COVID-19 mandate for businesses, seeking to stop the administration from implementing the mandate.

All 50 GOP senators, led by Sen Mike Braun (R-Ind.), joined to file their protest of the executive rule under the Congressional Review Act (CRA). The mandate is expected to impact millions of workers.

The rule published through the Occupational Safety and Health Administration (OSHA) earlier this month orders businesses with at least 100 employees to require their workers to get vaccinated or undergo regular testing by Jan. 4, although it faces legal challenges. Republicans have said this rule represents federal government overreach and violates American workers’ civil liberties. The resolution was referred to the Senate Health, Education, Labor and Pensions (HELP) Committee, and a floor vote could come as early as December.

“Republicans are united against President Biden’s vaccine-or-test mandate for businesses, but this federal overreach is not a partisan issue, and the consequences of this mandate are affecting Americans in all 50 states,” Braun said in a statement. The filing aligns with a challenge introduced in the House by Republicans, led by Rep. Fred Keller (R-Pa.).

With narrow Democratic majorities in the House and Senate, the effort is expected to be unsuccessful, but the vote could prove difficult for vulnerable incumbents up for reelection.

The Biden administration’s vaccinate-or-test requirement is estimated to impact more than 84 million workers, with businesses set to face fines of up to $136,532 for “willful violations.”

Braun, the ranking member of a Senate panel on employment and workforce safety, originally announced Republicans’ plans to challenge the executive rule earlier this month.

Several states, employers and religious groups filed lawsuits against the highly debated rule before the legal battle was transferred to a Cincinnati-based federal appeals court this week.

Biden administration officials seek to request the 6th Circuit Court of Appeals to reimplement the mandate after it was temporarily halted by the 5th Circuit Court of Appeals.

Officials have cited mandates as effective in boosting vaccination rates, in the hopes of increasing the stagnating national rate.