Republicans in the state Senate succeeded in blocking the bill from being referred to committee, though the measure's sponsor, Sen. Heather Stearns, D-Chicago, pledged when she tries again Thursday it will have enough support to reach a full Senate vote, the Chicago Tribune said.
The bill is one of several complicated issues remaining before the state legislature in the waning days of the term. New lawmakers are set to be sworn in Wednesday and the sitting legislature is also considering pension reform and the approval of casino gambling in Chicago.
The gay marriage push has ratcheted up both high-profile support and opposition from religious leaders.
Cardinal Francis George of Chicago wrote from the College of American Bishops to Illinois priests, saying a same-sex marriage bill would create a "legal fiction."
"The state has no power to create something that nature itself tells us is impossible," the church leader wrote to priests.
A celebrity push was underway backing the legislation to make Illinois the 10th state to allow gays and lesbians to marry. Jesse Tyler Ferguson, who plays Mitchell, half of the gay couple on the hit sit-com "Modern Family" said he hoped lawmakers would pass the bill.
"I'm looking forward to raising a family with [my fiance Justin Mikita] and having our kids grow up in an equal America," Ferguson said. "I had a hard time coming out and certainly had struggles with my parents. ... If the 12-year-old me had been able to turn on the TV and see a sitting president say he supports marriage equality, it would have made all the difference for me and certainly given me a lot of hope."
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