All 50 Senate Republicans are expected to back a long-shot formal challenge to President Biden’s vaccine mandate for private businesses on Wednesday, with the leader of the effort describing the rule as “an unconstitutional invasion.”  

The rule instituted by the Occupational Health and Safety Administration requires any private business with 100 or more workers to mandate that workers be fully vaccinated against the coronavirus by Jan. 4 or face weekly testing and mask-wearing requirements.  

According to Fox News, which first reported on the maneuver, Sen. Mike Braun (R-Ind.) is expected to introduce a joint resolution of disapproval under the Congressional Review Act.  If both houses of Congress approve the resolution and it is signed by the president — or if both houses override a presidential veto — the OSHA rule would be invalidated.  

The effort is unlikely to succeed since both the House and Senate are controlled by the Democrats and the White House has touted the vaccine mandate since announcing it this fall.  

Earlier this month, Braun announced that 41 Republican senators would support a resolution of disapproval, while the other nine were waiting for OSHA to formally release the rule. The agency announced the mandate Nov. 4  “President Biden’s vaccine mandate is an unconstitutional invasion of what should be a personal medical decision for every American and an affront to the rights of 80 million American workers,” Braun told Fox News.  

“Today, my Republican colleagues and I will formally challenge this federal overreach, and I urge the Senate to vote in favor of this disapproval resolution when it comes to the Floor for a filibuster-proof, simple-majority vote in early December.”  Businesses covered by the mandate employ approximately 84 million Americans, according to the White House. Employers who do not comply could face fines as high as $14,000 for each violation.  

On Tuesday, the House Freedom Caucus urged Speaker Nancy Pelosi (D-Calif.) to refuse to fund the executive branch until the order is rescinded.  

“President Biden and administration officials on his behalf have issued multiple executive orders and directives mandating COVID-19 vaccinations under threat of retribution that will cause the loss of livelihoods and endanger Americans,” the caucus wrote in a letter obtained by Fox News.  

“Federal vaccine mandates will only further divide America and harm our national security,” the letter continued. “For example, thousands of men and women in uniform are thus far choosing not to meet the recent COVID-19 vaccination requirements imposed by DoD. It is absurd to threaten to discharge — honorably or dishonorably — anyone in our military for making that choice,” the letter continued.  

More than 30 federal lawsuits have been filed challenging the mandate. On Tuesday, officials announced that the legal cases would be combined into a single challenge and heard by the Cincinnati-based 6th Circuit Court of Appeals.