The state of Texas' announcement that it was flagging tens of thousands of registered voters for citizenship checks was met with dismay among civil rights attorneys and voting rights advocates, who said it echoed efforts around the country to remove eligible voters from the rolls.

Now, several prominent civil rights groups are warning that following the state's recommended procedure for verifying those voters' citizenship could violate federal law.

Lawyers with 13 organizations — including the Texas Civil Rights Project, the ACLU of Texas, the League of Women Voters of Texas and the NAACP Legal Defense Fund — are demanding that the state rescind an advisory sent to local election officials regarding the individuals whose citizenship status the state says the counties should consider checking. In a letter sent Monday, the groups requested a response by Jan. 30, claiming that the state's data was flawed and demanding more information about the methodology it used.

Some of the groups are considering litigation against the state, said Beth Stevens, voting rights legal director for the Texas Civil Rights Project.

The letter comes three days after the Texas secretary of state’s office announced it would send local election officials a list of 95,000 registered voters who had provided the Texas Department of Safety some form of documentation, such as a green card or a work visa, that showed they were not citizens when they were obtaining driver’s licenses or an ID cards.

“Using such a data set to review the current citizenship status of anyone is inherently flawed because it fails to account for individuals who became naturalized citizens and registered to vote at any point after having obtained their driver license or personal identification card,” the lawyers wrote.

In their letter, the groups point to efforts in Florida that used similar methodology to create a list of approximately 180,000 registered voters that officials claimed were noncitizens based on records used when they obtained driver's licenses. That fight ended up in federal court after more than 2,600 were mistakenly removed from the rolls after being classified as noncitizens. About 85 voters "ultimately proved actionable," the lawyers wrote.

Although top Republican officials, including President Donald Trump, raised unsubstantiated claims of voter fraud, it’s possible that some of the individuals flagged by the state could have become naturalized citizens since they obtained their driver’s licenses or ID cards.

58,000 non-citizens voted in Texas, with 95,000 non-citizens registered to vote. These numbers are just the tip of the iceberg. All over the country, especially in California, voter fraud is rampant. Must be stopped. Strong voter ID! @foxandfriends — Donald J. Trump (@realDonaldTrump) January 27, 2019

Legal permanent residents, also known as green card holders, who become naturalized citizens after obtaining driver’s licenses are not required to update DPS on their citizenship status, according to voting rights lawyers. More than 30,000 immigrants in Texas were approved to become naturalized citizens in the first half of 2018. More than 52,000 were approved in 2017.

By law, counties are not allowed to automatically revoke a voter’s registration. Because the names sent to counties should be considered “weak” matches, counties may choose to verify the eligibility of the individuals flagged, which would require them to send notices asking for proof of citizenship within 30 days.

At the time of the announcement, Secretary of State David Whitley — whose office did not immediately respond to a request for comment regarding the demand letter — cited the need for “accuracy of our state’s voter rolls” to ensure the “integrity and efficiency of elections.”

But in their letter, the civil rights groups indicated the state could be putting tens of thousands of U.S. citizens on a pathway to be dropped off the rolls. They asked the secretary of state's office to address several questions regarding the method used for identifying the 95,000 individuals and whether it plans to take any steps to ensure that "any further investigation or mass purges does not become a vehicle for any kind of profiling on the basis of race, ethnicity, or political affiliation."

In another letter sent to local election officials, the groups urged them not to take action until the secretary of state's office provided more information on how it compiled the list of registered voters it flagged and how it would ensure that lawfully registered naturalized citizens wouldn't be targeted.

Later on Monday, the Mexican American Legal Defense and Educational Fund sent its own warning to counties that they ran the risk of violating the U.S. Constitution and federal laws if they challenged the eligibility of voters “simply because they were not U.S. citizens in the past.”

“The fact that a permanent resident immigrant lawfully obtains a driver’s license in Texas, and later naturalizes, should not cause you to scrutinize that voter’s eligibility any more than the eligibility of a native-born U.S. citizen,” Nina Perales, MALDEF’s vice president of litigation, wrote in the letter. “MALDEF urges you NOT to use this list of names from the SOS to send voter challenge letters, absent additional evidence regarding the current citizenship status of the voter.”