Several Republican senators voiced concern Monday over what they say is a weakening of citizenship standards when it comes to determining whether immigrants are over-relying on government aid like food stamps.

The ranking members of the Senate Budget, Judiciary, Finance, and Agriculture committees sent a letter to Secretary of State Hillary Clinton and DHS Secretary Janet Napolitano questioning promotional materials produced by USDA and distributed at Mexican consular offices designed to encourage food stamp use.

The senators say the materials state that a reliance on Supplemental Nutrition Assistance Program benefits, commonly known as food stamps, will not be taken into account when considering the merits of a visa application or status adjustment.

That isn't sitting well with Republicans, who note in the letter, "It has long been a sound principle of immigration law that those who seek citizenship in this country ought to be financially self-sufficient. We were thus shocked to discover that both the State Department and DHS exclude reliance on almost all governmental welfare programs when evaluating whether an alien is likely to become a public charge."

Sen. Jeff Sessions, R-Ala., the ranking member on the Senate Budget Committee has been a frequent critic of the U.S./Mexico partnership. He charges that it is possible for illegal immigrants to receive benefits by claiming legal status. He says that a screening program to prevent illegal aliens from accessing benefits is currently optional and not widely utilized.

The senators are seeking an explanation for the policy change and want to know how many visa recipients later became public charges.

The USDA has stressed that illegal immigrants, though, are not eligible for the program, and has defended its partnership with Mexico as a way to inform Mexican immigrants about the program "to help reduce hunger in America." The partnership was established in 2004.