Gay marriage would be banned in Indiana and the state would be barred from recognizing civil unions under a proposed constitutional amendment approved Wednesday by a state Senate committee.

On a party-line vote, the Senate Judiciary Committee approved the plan 7-3 after Republicans rejected arguments that a clause prohibiting civil unions could threaten the ability of employers to offer domestic partner benefits. The bill was sent to the full Senate for debate.

State law already bans gay marriage, and the statute has been upheld by state courts, but amendment supporters said a constitutional change would prevent future courts from overturning the ban.

Sen. John Broden, D-South Bend, said he didn't understand why lawmakers wanted to prevent future state Legislatures from considering whether to allow civil unions. Broden also echoed concerns from business leaders, including Indianapolis-based Eli Lilly and Co. and Columbus-based Cummins Inc., that the amendment could hurt their ability to recruit employees and prevent them from providing health insurance and other benefits to same-sex couples.

"I have no confidence that we aren't banning domestic partnership benefits here," Broden said.

Sen. Dennis Kruse, R-Auburn, said the measure wasn't meant to affect any benefits offered by private companies — or by state universities or local governments. Kruse said health benefits for domestic partners haven't been prohibited in the 30 states with similar constitutional amendments on marriage.

"It has not happened any place in the United States and there's no reason to think that's going to happen in Indiana," he said.

The committee rejected, along party lines, a proposal from Sen. Tim Lanane, D-Anderson, that would have limited the constitutional ban to same-sex marriages and left the door open for future recognition of civil unions. Lanane said it was a middle road, arguing that the public was becoming more accepting of civil unions.

But if attitudes are changing about gay marriage, countered Sen. Brent Steele, R-Bedford, then amendment opponents shouldn't fear the question going before voters for a statewide referendum.

That could be at least three years away. If the proposed amendment is ultimately approved by the Legislature this year, the House and Senate would have to approve it again in either 2013 or 2014 before it could appear on the 2014 ballot.

Opponents plan to continue arguing that the amendment is unnecessary and could hurt the state's image, said Rick Sutton, president of Indiana Equality Action, a coalition of groups against the proposal.

"We don't need to contribute to the brain drain in this state," Sutton said. "Young people are voting with their feet on issues like this and we need to keep the brightest minds here."

A similar amendment banning gay marriage passed the General Assembly in 2005, when Republicans controlled the House and Senate. But Democrats gained a House majority in 2006, and the proposal didn't clear the chamber again while they held power, so the process had to start over.

The Republican-led House voted in favor of the amendment last month.

More than 40 states prohibit same-sex marriage and more than half of those prohibit it through their state constitutions.