Eli Lilly's director of corporate responsibility Robert Smith speaks during the announcement of the new group "Freedom Indiana" on Aug. 21, 2013, in Indianapolis. An alliance of Indiana-based employers and human rights groups is launching a statewide movement to defeat passage of an amendment that would write the state’s ban on same-sex marriage into the constitution. Darron Cummings/AP

INDIANAPOLIS — With gay marriage now legal in 13 states and Washington, D.C. — and two more, Hawaii and Illinois, a governor's signature away from joining their ranks — there is a renewed effort in some other states to bar same-sex couples from achieving legal recognition.

In Indiana, for instance, lawmakers have already passed a ban on gay marriage and civil unions, but the state’s Republican-controlled legislature wants to strengthen it further with a constitutional amendment.

In fact, a constitutional amendment to ban gay marriage has been brought up in Indiana’s state legislature every year since 2004 — and this year is no different.

The latest attempt, however, has the backing of lawmakers from both parties. It's a proposed amendment to the state's constitution in the vein of the federal Defense of Marriage Act, or DOMA, which the U.S. Supreme Court struck down earlier this year.

It would warrant that only marriage between a man and a woman “will be valid or recognized as a marriage” in the state, and “a legal status identical or substantially similar to that of marriage for unmarried individuals” also won’t be considered valid or recognized.

If passed by Indiana’s general assembly, House Joint Resolution 6 (HRJ 6) would be sent to voters for a referendum in November 2014.

The recent approval of same-sex marriage in the adjacent state of Illinois could bolster supporters of marriage equality, although Indiana's other bordering states — Michigan, Ohio and Kentucky — all ban same-sex marriage in their constitutions.

Opponents say turning the ban already on the books into a constitutional amendment would make it more difficult to ever win equal rights for gay couples.

When Beth Applegate and her partner, Trish Kerle, moved back to Applegate’s hometown of Bloomington, Ind., three-and-a-half years ago, the state legislature had already been debating gay marriage for years.

"I think it’s not surprising that the Indiana legislature would attempt to do this again,” said Kerle, adding that there is a conservative political base that would expect lawmakers to pursue a ban on gay marriage.

"Allowing same-sex couples to be married has implications for inheritance, tax … social security, pensions — a number of very basic benefits that heterosexual couples take for granted,” said Applegate.

There is growing opposition to the constitutional amendment, notably on the part of Indiana University, which this week became the first public educational institution to openly support equal rights and speak against the amendment.

“This resolution, which would codify something in the state constitution which is inherently unequal, just isn't something we want to see happen,” said Indiana University spokesman Mark Land. "We recruit for the best talent everywhere around the world, and anything that says Indiana isn't welcoming of people of diverse backgrounds makes our job more difficult to get that talent.”

Some of the state’s largest employers, like pharmaceutical company Eli Lilly and shopping center giant Simon Malls, have also joined a coalition in opposition to the amendment.

The Indiana Family Institute has spoken in favor of the amendment on its website, but declined to be interviewed. A spokeswoman for the Indiana House of Representatives Republican Caucus offered no comment.

For couples like Applegate and Kerle, they most want to be, as Applegate says, “a full-fledged citizen of this great Hoosier land and the United States and to be treated as such — and to have equal protection is important to me."

In order to move onto the state ballot, the resolution must pass both the Indiana House and the Senate twice; it already passed both back in 2011. If it passes again this session, it could be put to a public vote in November of next year.