Low-income citizens, backed by antipoverty groups, filed a class action that challenges a federal law requiring proof of citizenship in exchange for benefits under the government's Medicaid health insurance program for the poor. Critics say the law, set to go into effect July 1, will hurt the vulnerable who may be unable to provide original documents like birth certificates. Those most in jeopardy are those in nursing homes, with mental and physical disabilities, and the victims of natural disasters.

The proposed class-action lawsuit, filed in Federal District Court in Chicago, argues the law unconstitutionally violates the Fifth Amendment's due-process guarantee by arbitrarily requiring documents and imposing deadlines.

The suit names Michael Leavitt, secretary of the U.S. Department of Health and Human Services, as defendant.

"Medicaid coverage will be delayed or denied for many," according to a recent analysis by the nonprofit Kaiser Family Foundation. "Obtaining required documents may be difficult and costly for low-income citizens," the report found.

One of the lawsuit's plaintiffs is 95 year-old Ruby Bell, who was born in 1911 in Arkansas and does not have a birth certificate. Bell now lives in a nursing home in Northern Illinois, but the county she came from did not start keeping certificates until 1914 and she may not be able prove citizenship under the law, her lawyer said.

Medicaid recipients are now required to be U.S. citizens, but documentation is only required of those under suspicion.

The lawsuit seeks to represent low-income citizens who currently receive Medicaid.