Sen. David Vitter, a Louisiana Republican, is demanding the 2010 Census ask about immigration status in order to “prevent states from counting” those who entered the country illegally.

Sen. Vitter announced today he had introduced an amendment to an appropriations bill that funds the Census Bureau and other government departments. If passed, Vitter’s amendment would require the U.S. Census to always ask about respondents’ citizenship and immigration status.

Writing at the conservative blog Big Government, Vitter said the amendment is “designed to help us identify illegal aliens, primarily to prevent states from counting them for the purposes of determining population levels, and other data associated with the Census.”

The inclusion of undocumented immigrants in Census data, Vitter says, has allowed some states to gain additional congressional seats at the expense of other states.

“I don’t believe that this is what our founding fathers had in mind when they laid out our current system of representation,” he writes in his blog post.

Utah Republican Sen. Bob Bennett has also backed Vitter’s proposal (he’s shown in a video at the end of this post making a floor speech on the issue), according to Talking Points Memo.

Other politicians, most notably Republican Rep. Michele Bachmann of Minnesota, have also publicly criticized the decennial Census for including undocumented immigrants.

Unlike previous counts, which used forms of different lengths, the 2010 Census will rely on a “short form” questionnaire, which does not ask about immigration status.

The short forms are being mailed out in Spanish and several other languages to boost immigrants’ participation.

The Census Bureau has gone out of its way to assure immigrants, whatever their status, that its data is confidential, and a breach of privacy is met with stiff penalties stipulated by federal law.

It also has assured immigrant communities its data will not be shared with other federal agencies, like Immigration and Customs Enforcement or ICE.