Thomas John Paprocki, the Roman Catholic bishop of Springfield, Illinois, has urged Catholics to oppose a proposed gay marriage law because otherwise they would be subject to “harsh discriminatory treatment.”

Illinois lawmakers are debating the issue during a lame-duck session, which ends on Tuesday. But after a tumultuous path in the Senate, some outlets are reporting that supporters have decided to postpone their push until after the new legislative session begins on Wednesday.

(Related: Gay marriage bill clears Illinois Senate committee.)

In a pastoral letter dated January 2, Paprocki joined other Illinois Catholic leaders in describing gay nuptials as against nature.

(Related: Cardinal Francis George: Gay marriage is unnatural.)

“All people of goodwill, and especially Christ's faithful committed to my pastoral care in the Diocese of Springfield in Illinois, should resolutely oppose this bill and make their opinions known to their representatives,” Paprocki wrote.

“[N]either two men nor two women – nor, for that matter, three or more people – can possibly form a marriage. Our law would be lying if it said that they could.”

“The basic structure of marriage as the exclusive and lasting relationship of a man and a woman, committed to a life which is fulfilled by having children, is given to us in human nature, and thus by nature's God.”

“There is no possible way – none whatsoever – for those who believe that marriage is exclusively the union of husband and wife to avoid legal penalties and harsh discriminatory treatment if the bill becomes law. … After all, we would be people who, according to the thinking behind the bill, hold onto an 'unfair' view of marriage. The state would have equated our view with bigotry – which it uses the law to marginalize in every way short of criminal punishment.”