MONTGOMERY — The Alabama Senate approved a proposed constitutional amendment Thursday that would add the state’s right-to-work law to the document, a change that proponents say could attract more industry but that opponents call anti-middle class.

The Senate passed the legislation 21-10, with Republicans voting yes and Democrats no. The vote came after Republicans blocked stalling tactics by Democrats.

The legislation now goes to the House. If passed by the House, it won’t take effect unless approved by Alabama voters in next year’s general election. It could become the second amendment to Alabama’s constitution pushed by business groups and Republican legislators who say they want Alabama to be a “y’all come” state.

The right-to-work law provides that employees can’t be required to join a union or pay union dues as a condition of employment. The proposed constitutional amendment mirrors that by saying, “An employer may not require a person, as a condition of employment or continuation of employment, to pay dues, fees or other charges of any kind to any labor union or labor organization.”

The sponsor, Republican Sen. Gerald Dial of Lineville, said the right-to-work law has helped Alabama recruit many industries, particularly large auto plants, and it needs to be protected by being put in the state constitution where it can’t be changed with only a vote of the Legislature.

Democratic Sen. Bobby Singleton of Greensboro said putting it in the constitution is unnecessary because no one has tried to repeal the right-to-work law.

“Times change in this legislative body,” said Dial, who noted he had been a Democrat and an independent prior to becoming a Republican.

William Canary, president of the Business Council of Alabama, said Alabama’s right-to-work status helps attract new jobs, and protecting it in the constitution is important.

“Existing industries and companies looking to potentially locate here can be confident that Alabama will remain a business-friendly state,” he said.

Al Henley, president of the Alabama AFL-CIO, said the right-to-work law keeps the standard of living low for Alabama’s middle class.

“Senator Dial and the anti-middle class state senate should create ideas and enact laws to make the middle class stronger instead of trying to weaken it.

Putting bad laws in the constitution is a horrible idea,” Henley said.

The proposed constitutional amendment comes after voters approved another amendment in November 2012 that prohibits the organization of a union in Alabama by having a majority of employees sign a card. Instead of a card check process, a vote by secret ballot is the only method available.