The battle over voting rights will expand this week as lawmakers in Missouri are expected to support a proposed constitutional amendment to enable election officials to require proof of citizenship from anyone registering to vote.

The measure would allow far more rigorous demands than the voter ID requirement recently upheld by the Supreme Court, in which voters had to prove their identity with a government-issued card.

Sponsors of the amendment — which requires the approval of voters to go into effect, possibly in an August referendum — say it is part of an effort to prevent illegal immigrants from affecting the political process. Critics say the measure could lead to the disenfranchisement of tens of thousands of legal residents who would find it difficult to prove their citizenship.

Voting experts say the Missouri amendment represents the next logical step for those who have supported stronger voter ID requirements and the next battleground in how elections are conducted. Similar measures requiring proof of citizenship are being considered in at least 19 state legislatures. Bills in Florida, Kansas, Oklahoma and South Carolina have strong support. But only in Missouri does the requirement have a chance of taking effect before the presidential election.

In Arizona, the only state that requires proof of citizenship to register to vote, more than 38,000 voter registration applications have been thrown out since the state adopted its measure in 2004. That number was included in election data obtained through a lawsuit filed by voting rights advocates and provided to The New York Times. More than 70 percent of those registrations came from people who stated under oath that they were born in the United States, the data showed.