Last year Colorado adopted a particularly tough regime, including a requirement that all government contractors run new hires through E-Verify--an otherwise voluntary federal online service that checks if the Social Security or immigration id numbers that new hires provide are legit.
The states' plans require voters to present photo ID like a driver's license or passport to vote, a measure endorsed by the Commission on Federal Election Reform headed by President Jimmy Carter and former Secretary of State James Baker in 2005 to protect the integrity of the ballot.