Ronald Klain, the White House chief of staff, faced criticism on social media Thursday after he retweeted a post that seemed to praise the Biden administration for pulling off the "ultimate work-around" for a national COVID-19 vaccine requirement.

President Biden announced proposed rules that would force private-sector employers with more than 100 workers to either require them to be fully vaccinated or mandate that they undergo weekly tests. Biden referred to the mandate as a "new action plan." The rules would be enforced by the Occupational Safety and Health Administration (OSHA).

Businesses that do not comply would face fines up to $14,000 per offense, an administration official told The Associated Press. The mandate is expected to affect as many as 100 million Americans.

Klain retweeted MSNBC’s Stephanie Ruhle, who posted, "OSHA doing this vaxx mandate as an emergency workplace safety rule is the ultimate work-around for the Federal govt to require vaccinations."

The New York Times pointed out that OSHA is tasked with overseeing workplace safety and has the authority to "quickly issue a rule, known as an emergency temporary standard, if it can show that workers are exposed to a grave danger and that the rule is necessary to address that danger. The rule must also be feasible for employers to enforce."

Ted Cruz reacts

Sen. Ted Cruz, R-Texas, a critic of Biden’s announcement, retweeted a post warning Klain that courts consider intention when hearing cases, and the retweet could prove to be problematic during future challenges.

"Important," Cruz tweeted. "Foolish RT from WH chief of staff. He said the quiet part out loud. Biden admin knows it’s likely illegal (like the eviction moratorium) but they don’t care."

The senator was referring to the Supreme Court’s ruling last month that blocked the Biden administration from continuing a temporary eviction ban in place due to the coronavirus. The court said that the Centers for Disease Control and Prevention (CDC) lacked the authority to reimpose the moratorium earlier that month without congressional approval.

Klain did not immediately respond to an after-hours email from Fox News.

Republican members of Congress and state governors promised to challenge the mandate.

Arizona Republican Gov. Doug Ducey vowed to "push back" against Biden.

"This is exactly the kind of big government overreach we have tried so hard to prevent in Arizona — now the Biden-Harris administration is hammering down on private businesses and individual freedoms in an unprecedented and dangerous way," Ducey wrote. "This will never stand up in court."

Biden was praised by supporters for striking a more urgent tone. These supporters insist that one of the key reasons cases are spiking in the U.S. is due to the 80 million who have refused the jab. 

CLICK HERE TO GET THE FOX NEWS APP

"My message to unvaccinated Americans is this: what more is there to wait for? What more do you need to see? We have made vaccinations free, safe, & convenient. The vaccine is FDA approved. Over 200 million Americans have gotten at least one shot. We have been patient, but our patience is wearing thin, and the refusal has cost all of us," Biden said.

The Associated Press contributed to this report.