Two state lawmakers from Philadelphia are to introduce a bill to legalise same-sex marriage in the US state of Pennsylvania.

Brian Sims and Steve McCarter, both Democrat members of the Pennsylvania House of Representatives, will formally announce the introduction of the Pennslyvania Marriage Equality Act during news conference at 10am local time (3pm BST).

Though the state’s Republican governor is a staunch opponent of equal marriage, Representatives Sims and McCarter are encouraged by growing support for the measure and say that more than 30 lawmakers have signed onto the bill as co-sponsors, The Philadelphia Daily News reports.

Representative Sims, who last year became the first openly gay candidate to be elected to the Pennslyvania state legislature, said: “It was really in June when Representative McCarter and I, who’ve been talking about this for a while, took the lay of the land and found our colleagues were ready to support this issue. We’ve been seeing this growing support, so it’s the right time.”

Representative Sims continued to say that expects the bill to gain approval eventually, if not immediately.

“Like most pieces of legislation, they get introduced and they get moved around, shuffled around and debated. I expect that to be the case with this bill,” he said. “I don’t have some pie-in-the-sky idea this is going to sail through the Legislature.”

He added, however: “This bill is going to become law sooner than later.”

Ted Martin, executive director of gay rights organisation Equality Pennsylvania, welcomed the introduction of the bill, but recognised that its passage would not be easy given Pennslyvania’s state statute banning the recognition of same-sex marriage.

He said: “In a state where you can still be fired for being gay, it’s going to be challenging. But I say in the same breath that you also never know what’s going to happen – who knows?”

A Pennslyvania county which was last month ordered to stop issuing marriage licences to same-sex couples announced it is appealing against the decision this week.

Currently, thirteen US states (California, Connecticut, Delaware, Iowa, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New York, Rhode Island, Vermont, and Washington), the District of Columbia and several counties in New Mexico allow same-sex marriage.

Courts are currently litigating on the issue in the states of New Jersey and New Mexico.

Earlier this week, New Jersey Governor Chris Christie filed an appeal against a ruling that equal marriage be made legal in the state.