HELENA (AP) — A Montana law firm is suing the state over a rule that bans businesses from requiring COVID-19 vaccinations for their employees.

This is the second lawsuit challenging the only law in the U.S. that prevents employers from mandating workers get vaccinated against the coronavirus.

Netzer Law Office, which has five employees and locations in Sidney and Billings, said the law passed earlier this year by the Republican-controlled Legislature interferes with the business' "choice in determining how best to provide a safe and healthy environment." The law office is represented in the suit by Joel Krautter, a former Republican state lawmaker.

The law — which applies to all vaccinations — says that requiring vaccines as a condition of employment is discriminatory and violates the state's human rights laws.

The suit filed Tuesday in district court in Richland County states that the new law violates the Montana Constitution, which guarantees the right to "a clean and healthful environment." In addition to asking for the law to be deemed unconstitutional, the plaintiffs are asking for a preliminary injunction staying the enforcement of the law while the legal challenge is underway.

The suit names state Republican State Attorney General Austin Knudsen and Commissioner of Labor and Industry Laurie Esau as defendants.

"Attorney General Knudsen will defend Montana's law. No one should be treated differently because of their vaccination status," said spokesperson Emilee Cantrell.

Esau's spokesperson did not immediately respond to requests for comment.

A lawsuit challenging the same law was filed last month by medical providers and Montana residents with compromised immune systems, who argued the law violates federal requirements for safe workplaces and reasonable accommodations for people with disabilities.

Last month, President Joe Biden asked the Occupational Safety and Health Administration to write a rule requiring employers with at least 100 workers to mandate they get vaccinated against COVID-19 or submit to weekly testing.

Montana Gov. Greg Gianforte has said he would challenge that rule, calling it unlawful and un-American. The Republican has encouraged people to get vaccinated against COVID-19 but has maintained it should be a voluntary decision.