WASHINGTON – Gov. Haley Barbour (R-MS), a rumored 2012 presidential contender, lobbied on behalf of Mexico last decade for a program that would have assisted unauthorized immigrants with gaining permanent residency.

That's according to a report in TIME's Swampland blog by Michael Scherer, who obtained State Department filings revealing that Barbour's lobbying firm -- Barbour, Griffith & Rogers -- lobbied for Mexico on the program in 2001 and 2002.

Barbour's firm was paid $35,000 a month by Mexico, plus other expenses.

The revelation could create political problems for the Mississippi Republican, the current chairman of the Republican Governors Association and important player within the GOP, if he decides to run for president. The Republican base is fiercely opposed to any kind of legalization program for unauthorized immigrants.

Barbour's firm helped Mexico build Congressional support for a bill relating to Section 245(i) of the Immigration and Nationality Act, which would have allowed undocumented immigrants in the United States to attain legal visas and permanent residency based on job skills and family connections. They would have to pay a fine but would not have to return to their country of origin.

The effort was denounced by conservative critics as a "mini-amnesty" program.

“This amnesty loophole allowed aliens who broke our laws to pay a $1,000 fine and go to the head of the line in front of prospective immigrants who complied with our laws,” wrote conservative Phyllis Schlafly in 2002.

A similar provision was eventually championed by the Bush administration in its attempts to overhaul immigration in 2006 and 2007. The legislation ultimately failed, with the legalization program serving as a dealbreaker for too many Republicans.

Barbour has largely embraced his lobbyist past, but his conservative supporters aren't likely to ignore this aspect of his lobbying, especially if Barbour seeks the Republican nomination for president.

He's widely considered a dark-horse candidate, garnering only a few percent of the Republican vote in most national polls.