Some of the plaintiffs, such as New York City Department of Education employees, a handful of Los Angeles county public employees and United Airlines workers, have argued that the mandates should be removed, questioning the rules' constitutionality and some contending their religious rights weren't observed.
So far, these arguments have not swayed judges who have almost all ruled in favor of the employer, or not issued long injunctions while they hear the case. And legal experts tell ABC News they don't expect different outcomes in courtrooms anytime soon.
Glenn Cohen, a health law and bioethics professor at Harvard Law School, told ABC News that strong legal precedent dating back to the early 20th century gives businesses and governments the legal backing to enforce the mandates.
"They're pretty weak," Cohen said of the lawsuits. "The judges that have denied them have come from across the political spectrum, and from across the country, because the plaintiffs' arguments don't have any weight."
Cohen and other scholars who have been monitoring the cases predict that there will be fewer suits against the mandates as more cases are thrown out. However, they warned that there is a potential court battle over how businesses accommodate religious exemptions for vaccinations because that issue hasn't been settled in the Supreme Court.
Cohen said that the 1905 Supreme Court Case Jacobson v. Massachusetts held that state legislatures are allowed to issue vaccine mandates. The 7-2 decision dealt with Massachusetts' vaccine mandate for the smallpox vaccine.
And a July 2021 ruling by the Department of Justice's Office of Legal Counsel also gave businesses the legal backing to invoke a COVID-19 vaccine mandate for their employees.
Dorit Rubinstein Reiss, a professor of law at UC Hastings College of the Law, who has written about the legalities of vaccine mandates in law journals, told ABC News that earlier COVID-19 vaccine mandate lawsuits argued that the orders were unconstitutional since the three available vaccines were only authorized for emergency use by the Food and Drug Administration (FDA).
None ended up being successful, she said.
That argument lost ground in courts after the FDA fully approved the Pfizer vaccine in August, she noted.
"If you're at the point where you are saying this is like the Nuremberg trials and the vaccines are experimental and could be dangerous, you don't have a good example," Reiss said.
Reiss said the reasonable accommodations provision of the Civil Rights Act of 1964 requires employers to make special accommodations to employees, such as those based on religious beliefs.
"It is a statutory right, not a constitutional right," she said.
Cohen, a former DOJ appellate lawyer, added that public and private employers have provided leeway for their members to get religious and medical exemptions, and for the most part have been accommodating. In some of the cases that Cohen observed that plaintiffs have used the religious exemption argument against their employer, but judges have dismissed the cases citing the lack of substantial evidence that their faith was targeted.
"They're claiming religious exemptions but the underlying religion in question doesn't provide an exemption," Cohen explained.
Potential battle over religious exemptions
One company's vaccine mandate policy, however, has led to what Cohen sees as an interesting court battle.
A group of United Airlines employees, including a pilot and flight attendant, filed a lawsuit last week against the airline over its vaccine mandate, contending that the company's policy of placing them on "an indefinite period of unpaid leave" for being unvaccinated hurt their livelihood. The plaintiffs claim they are refusing vaccinations because of their religious beliefs, the suit said.
United, which said over 98% of its staff complied with the mandate, defended its policy in a statement saying "vaccine requirements have been around for decades and have served to keep airline employees and customers safe."
Cohen said that the Jacobson case did not cover religious exemptions and the Supreme Court has yet to rule on how those exemptions play out with vaccine mandates. He said in the United lawsuit, the argument is centered on job accommodations for those unvaccinated employees and not the mandate itself, so there may not be a major game-changing ruling.
"We'll have to see how this plays out," he said. "If it turns out, at the end of the day, [United Airlines isn't] going to put them back on a plane, they are likely to face more litigation," he said.
Reiss predicted that the issue of religious exemptions will eventually reach the Supreme Court, but it's hard to know if the court will review a case. Last week, the Supreme Court denied a request by New York City education employees to hear their case against the city's vaccine mandate after several lower courts ruled against the plaintiffs.
Reiss and Cohen believe that as more cases are dismissed and judges issue strong rulings, attorneys won't have enough of a foundation to make successful cases.
"It will be easier for courts to point at the losses and make it easier to reject the new ones," Cohen said. "I think you'll see fewer attorneys taking up those cases too."
Reiss added that the mandates have shown to increase vaccination rates in public and private companies, especially in the days leading up to their employer's compliance deadline. In most cases, such as hospital systems in New York, North Carolina and California, vaccine rates among staff ended up over 95% when the deadline came.
"The mandates will have some impact regardless of what happens in the courts," Reiss said.