Alice Yi of Austin is frustrated when she thinks about the March primary election, in which her 92-year-old father tried to vote by mail, as he had many times before, but couldn't.

He could not remember what identification number he used to register to vote more than 30 years ago, she said. When he sent in his ballot application with the last four digits of his Social Security number, a rejection letter from the elections office said that number was not on file. Another letter later said her father, who is legally blind in one eye, failed to fill out other details, such as specifying which ballot he needed.

By the third attempt, Yi, his caregiver, worried her father's application would not make it before the deadline and he would be unable to cast a ballot. So she took him to vote in person, for the first time in years.

Yi's father was just one of thousands of Texans who attempted to vote by mail in the March primary but collided with the Texas GOP's restrictive 2021 voting law, known as Senate Bill 1. When voting by mail, the new law requires voters to write their driver's license number, personal identification number or the last four digits of their Social Security number on their mail ballot application and mail ballot envelope — whichever number they originally used to register.

In fact, the mail-in applications and ballots of Asian, Latino and Black Texans were rejected because of the new ID requirement at much higher rates than those of white voters, according to a study released Thursday by the Brennan Center for Justice, a nonpartisan law and policy institute. The office of the secretary of state declined to comment, citing pending litigation over SB 1.

Although researchers couldn't determine the exact cause of the disparities, experts and advocates say that in addition to the voting law's restrictions, existing factors rooted in systemic racism, such as lack of resources in people's native languages and other socioeconomic barriers, likely played a role in the high rejection rates.