(Reuters) - After two weeks of protests at the Utah state capitol, the state has banned collective bargaining for teachers, police officers, firefighters and other public employees, a move unions have vowed to fight.

Utah's Governor Spencer Cox, a Republican, signed the ban even as protests continued outside the state capitol in Salt Lake City demanded he veto the controversial bill.

Federal law protects the collective bargaining rights of workers in the private sector, but determining labor law for public employees is up to the states.

Supporters of the law argued that labor unions were inherently political and that allowing them to engage in collective bargaining on behalf of public employees presented a conflict of interest and could burden the taxpayer.

Scores of members of the Utah's largest teachers union, the Utah Education Association, which represents 18,000 public school educators, held a silent protest outside Cox's office as he signed the bill.

In a statement following the governor's signature, the association said Cox and the state lawmakers had "ignored the voices of thousands."

Opposition groups promised to fight on with a possible ballot measure to overturn the law. The law, which its critics say is anti-labor, goes into effect July 1.

"Looks like Utah will become the most anti-labor state in America," Jack Tidrow, president of the Professional Firefighters of Utah said in a statement. "Pathetic."

The bill's sponsor, Rep. Jordan Teuscher, a Republican, said in a statement Saturday that Republican lawmakers were pleased to see the governor sign the bill.

"This bill upholds democratic principles and expands individual freedoms for Utah's dedicated public employees," he wrote, adding that the law does not eliminate unions.

"Teachers and other public employees will still have the right to organize, advocate for themselves, and receive union support," he wrote.

Teuscher introduced the bill January 18, and it passed the house just over a week later and the Senate February 6.

Republicans have 61 seats in the Utah legislature, giving them a supermajority.