The bishops, gathering in Los Angeles in preparation for a general meeting Thursday through Saturday, were expected to discuss immigration and other issues.

Catholic leaders, who helped organize protests that have brought hundreds of thousands to the streets in recent months in favor of immigrants' rights, have long criticized an immigration reform bill passed by the House of Representatives in December.

That bill would build more fences along the U.S.-Mexico border, criminalize people who help the undocumented, and make being in the country illegally a felony, up from a misdemeanor.

On Wednesday, the bishops criticized pieces of an immigration bill passed by the Senate in May that included a path to citizenship for many illegal immigrants, but also fortifies the border by adding patrol agents and building more fences.

The bishops said fortifying the U.S.-Mexico border wouldn't stop the flow of illegal immigrants, which they argued could only happen by expanding programs to allow more foreigners to enter the country legally and work.

"The problem is not at the border, it's in the labor market," said Bishop Nicholas DiMarzio of Brooklyn, N.Y.

The bishops said the Senate's legalization plan, which has a three-tier system depending on how long an immigrant has been in country, was "unrealistic" and could open up the door to fraud and other abuses. They advocated a more inclusive program that wouldn't make distinctions.

On the border "we see persons who are being exploited by smugglers, and women and children who are dying in the desert," said Cardinal Roger Mahony, head of the Archdiocese of Los Angeles.