The Illinois House is expected to debate a gay marriage bill on Friday, the last day of the regular legislative session.

The proposed legislation, which stalled in the House after clearing the Senate on Valentine's Day, has the support of Democratic Governor Pat Quinn, who has pledged his signature.

On Thursday, groups lobbying for passage of the measure announced a Marriage Equality Rally to take place at the State House starting at 11AM Friday. Illinois Unites for Marriage was offering free passage to Springfield for activists in Chicago.

“FREE buses from Chicago to our marriage rally in Springfield tomorrow morning!” the group tweeted.

Appearing in Chicago on Wednesday, President Barack Obama referenced the bill.

“Here in Illinois, we've got a vote on same-sex marriage that's going to be coming up in the state Legislature,” Obama told donors at a fundraiser. “And I just want to say for the record it's something that I deeply support. I wrestled with this for a long time and I am absolutely convinced it is the right thing to do.”

Meanwhile, opponents of the legislation called on lawmakers to reject the bill.

In an open letter to House members, the conservative Thomas More Society said that the bill “provides a disaster for religious liberty, no matter which side of the same-sex marriage debate that one supports.”

The group lamented the bill's lack of religious exemptions for individuals and businesses.

“SB 10 provides no protections for individuals who make their living by providing goods and services for the celebration of weddings, such as cake bakers, florists, and venue owners,” the letter states. “Under SB 10, people of faith running these businesses would be faced with the choice of either closing their business or facilitating a ceremony that violates their religious beliefs.”

If the marriage law is approved, Illinois would become the 13th state to legalize such unions, the fourth this year and only the third in the Midwest.