The U.S. Conference of Catholic Bishops is urging the House to draft an immigration reform bill by the end of the year, saying it is a matter of "great moral urgency."

In a letter Thursday to House Speaker John Boehner, R-Ohio, Cardinal Timothy Dolan of New York, the group's president, said immigrants and their families are suffering because the current immigration system has failed.

"As pastors, we [the bishops] witness each day the human consequences of a broken immigration system," Dolan wrote. "Families are separated through deportation, migrant workers are exploited in the workplace and migrants die in the desert."

Dolan said that keeping illegal immigrants as a permanent underclass is a "stain on the soul of our nation."

"As a moral matter, our nation cannot continue to receive the benefits of the work and contributions of undocumented immigrants without extending them the protection of the law," he said. "Keeping these human beings as a permanent underclass of workers who are unable to assert their rights or enjoy the fruits of their labor is a stain on the soul of the nation."

Dolan added the House has responsibility to "debate and attempt to resolve public policy issues that challenge the nation."

The bishops' effort dovetails with a new push this week by labor unions and Hispanic advocacy groups to pressure individual House Republicans to address immigration reform.

The Democratic-controlled Senate passed a comprehensive immigration bill in June with significant bipartisan support. But the measure, which offers a path to citizenship for millions of immigrants who have entered the country illegally, has stalled in the Republican-led House.

House Republican leaders say they're not against tackling immigration reform but have hinted they prefer to do so in a piecemeal fashion. One of those major components would deal with increasing border security.

In response to the bishops' letter, Boehner spokesman Michael Steel said "the speaker has been very clear that he supports common-sense, step-by-step reforms to fix our broken immigration system."