Iowa Senate Majority Leader Mike Gronstal has once again vowed to block any attempt to ban gay marriage, the AP reported.

Social conservatives have rallied behind an amendment to the Iowa constitution that would limit marriage to heterosexual unions since an unanimous 2009 Iowa Supreme Court ruling legalized gay marriage.

Last year, the Republican-controlled House easily approved such an amendment, but Gronstal blocked the measure from reaching the Senate floor, angering conservatives who have threatened to oust him.

“People's rights should not be put to a popular vote,” Gronstal said. “We didn't put slavery to a vote of the people in Iowa. We didn't put the right to go to a school in your neighborhood to a vote of the people, and we didn't put the public accommodations law to a vote of the people in Iowa.”

Senate Minority Leader Jerry Behn, an opponent of marriage equality, argued that the issue was about “Iowans being allowed to vote.”

“The idea, the concept, is should the debate be allowed?” he said.

If lawmakers do not act this year, the earliest voters could see the measure on the ballot would be 2016.