Montana U.S. Sen. Jon Tester crossed party lines Wednesday to support a resolution that blocks a federal rule requiring vaccines or weekly testing for workers at private businesses with 100 or more employees.

Tester, a Democrat, and Sen. Joe Manchin of West Virginia voted with 50 Republicans to end the rule that is currently being challenged in court. It is unlikely the Democrat-majority House will take up the joint resolution, meaning the outcome will remain in the court’s hands.

Tester said the decision to break from his party fell squarely on feedback he had received from Montana businesses concerned about the rule’s impact on their workforce and the potential to lose valuable employees.

“It’s become so onerous for businesses … it wasn’t workable,” Tester said on a call with Montana press Thursday.

“I just thought this was too burdensome for them to have.”

Likewise, U.S. Sen. Steve Daines commented that the mandate had spurred an outpouring of critical feedback from Montana business leaders. The Republican from Montana has consistently pushed back against the Biden administration’s vaccine mandates, and in October he cosponsored the Stop Vaccine Mandates Act.

“Every so often Washington D.C. does something that lights up the phone lines. This is one of these moments,” Daines said following the vote. In Montana, he said, "this issue is what I hear about. This issue is a top-of-mind issue.”

“This is not about being anti vaccine. I was part of the Pfizer trial. I’m pro science and pro vaccine. But I’m anti mandate.”

UNDER THE federal rule, private companies with 100 or more workers must require their employees to be fully vaccinated against Covid or be tested for the virus weekly and wear masks on the job. The Occupational Safety and Health Administration said it would work with companies on compliance but would fine them up to more than $13,000 for each violation, though implementation and enforcement is suspended as the litigation unfolds.

Whitefish Mountain Resort CEO Dan Graves was among the Montana business leaders who shared their frustration with the mandate. In commentary provided by Daines’ office, Graves noted that staffing has been a challenge at the ski area, even without the mandate.

“I can’t afford to lose 10% let alone 30% [of the resort’s workforce], Graves said. “So it’s very concerning to me. If this vaccine mandate hits the first part of January, to start figuring it out and get it started is going to have to take place during Christmas season, which is our busiest time of year.

“We have not had our full compliment of staffing for well over a year, so it’s a real threat. If the intent is to close businesses or make them struggle, this is a good way to do it.”

Proof Research president KK Jense offered similar feedback, telling Daines’ office that the vaccine mandate had created “a lot of confusion for everybody” at the Flathead-based company.

“We respect people’s choices and rights,” Jense said, adding that Proof has taken many actions to keep the workplace safe during Covid.

While Tester opposes the mandate for private businesses, he said he still supports the requirement of Covid vaccines for health-care workers and federal contractors.

“The reason is that health-care workers are in the health-care business,” Tester said Thursday “We can’t afford to have [Covid] spread in hospitals.”

The mandates for health-care workers and federal contractors are both paused while they are challenged in federal courts.

The White House released a statement earlier this week stating that Biden's advisers would recommend he veto the joint resolution in the unlikely event it makes it to his desk.

“The president wants to see Americans back on the job, and Americans back at work should not face risk from those who are not vaccinated and who refuse to be tested," the White House said.

Covid-related deaths in the U.S. are running close to 1,600 a day on average. The overall U.S. death toll less than two years into the pandemic could soon reach 800,000.

The Associated Press contributed to this report.