DOVER, Del. (AP) — The state House on Tuesday narrowly approved a bill legalizing gay marriage in Delaware, barely a year after the state began recognizing same-sex civil unions.

The measure cleared the House on a 23-to-18 vote and now goes to the Senate, where supporters and opponents expect another close vote.

Democratic Gov. Jack Markell has promised to sign the bill if it passes the Democrat-led legislature.

“It’s the right thing to do,” said Markell, who met with supporters of the bill in his Legislative Hall office immediately after Tuesday’s vote, which saw five Democrats break ranks with their party and oppose the measure.

Rep. Michael Ramone of Newark was the only Republican to vote for the bill.

Under the proposal, no new civil unions would be performed in Delaware after July 1, and existing civil unions would be converted to marriages.

Supporters say couples in same-sex relationships deserve the same dignity and respect afforded to married couples.

“It’s about equal status,” said Mark Purpura of Equality Delaware, a gay rights group that drafted the legislation.

Opponents argue that same-sex marriage redefines and destroys the institution, and that same-sex couples in civil unions already have all the rights and benefits under state law that married couples have.

“What benefits are same-sex couples missing that this state can’t help them with?” asked Rep. Stephen Smyk, a Sussex County Republican.

Purpura noted that if the U.S. Supreme Court strikes down the Defense of Marriage Act, which bars legally married gay couples from receiving federal benefits, civil unions would not provide any protections or tax benefits under federal law to same-sex couples in Delaware.

Nicole Theis of the Delaware Family Policy Council said the bill is taking a fundamental building block of society and redefining it.

“Marriage is based on the truth that men and women are complementary, and the biological facts of reproduction,” Theis said.

While the bill does not force clerics to perform same-sex marriages that conflict with their religious beliefs, opponents warned that business owners who refuse to provide marriage-related services for same-sex couples could be subject to discrimination claims.

“If there’s an exemption for right of conscience, I don’t see it,” said Jordan Lorence an attorney with the Alliance Defending Freedom, a conservative religious liberties group.

Rep. Melanie George Smith, the prime sponsor of the bill, said state law already prohibits discrimination based on sexual orientation, and that the gay marriage bill does not change that in any way.

“We respect your right to believe what you believe,” she told fellow lawmakers who oppose the bill.

Republican Rep. Tim Dukes, a longtime Sussex County pastor who has performed hundreds of wedding ceremonies, concluded Tuesday’s floor debate by urging his colleagues to preserve “the greatest foundation that’s ever been established.

Dukes expressed concern that society has evolved to a point where if you oppose a person’s lifestyle, you are thought to either fear or hate the person, or that if you love someone, you support everything they say or do.

“Both are nonsense,” he said.

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