Chicago's Cardinal Francis George is urging parishioners to let state lawmakers know they oppose gay marriage.
George's letter to priests in the Roman Catholic archdiocese comes as Illinois legislators are poised to consider a bill that would legalize same-sex marriage.
"When there's a disagreement like this between the church and the state that it's very hard," Parishioner Marlene Robin said. "I think it's very difficult (to deal with)."
State Sen. Heather Steans and state Rep. Greg Harris could introduce the Religious Freedom and Marriage Fairness Act to legalize same-sex marriage as early as this week.
George wrote that allowing gay couples to marry would be "acting against the common good of society."
Previously, some clergy members sent a letter pushing for gay marriage and some of Illinois' top companies and executives have also voiced their support for the legislation after Chicago Mayor Rahm Emanuel asked CEO's to sign such a letter.
(Copyright 2013 by The Associated Press. All rights reserved. Quotes from ABC Newscall were used in this story.)