The Catholic Conference of Illinois is calling on lawmakers to reject a bill that would recognize gay and lesbian couples with civil unions.

The legislation, which is sponsored by openly gay Illinois State Representative Greg Harris, passed out of committee last spring. Governor Pat Quinn has said he wants to sign the bill into law this year.

Several high-profile Chicago mayoral candidates have also endorsed the bill, including former White House chief of staff Rahm Emanuel and former U.S. Senator Carol Moseley Braun.

In a statement released on Monday, Cardinal Francis George, the head of the Catholic Conference of Illinois and the outgoing president of the Conference of Catholic Bishops, said he's opposed to the measure.

“Everyone has a right to marry, but no one has the right to change the nature of marriage,” he wrote. “Marriage is what it is and always has been, no matter what a legislature decides to do; however, the public understanding of marriage will be negatively affected by passage of a bill that ignores the natural fact that sexual complementarity is at the core of marriage.”

“The enactment of marriage-like benefits in civil union legislation will intensify the legal attack on marriage,” he added.

Insiders say the bill could be put up for a vote as early as next week.