As the heat index hit 115 degrees on Monday, Karla Perez took a five-minute water break at a construction site in Dallas. Such rest breaks are required by the city, as they are in Austin.
But a change in Texas state law, which goes into effect in September, will wipe away those local requirements, leaving workers like Ms. Perez to count on their employers to provide time to rest and rehydrate. Right now, she gets three breaks a day. She dreads what the change might bring.
“Workers are going to die,” she said. “There’s no way around it.”
The legal change was part of a sweeping effort by the Republican-dominated State Legislature to exert control over its Democratic-led major cities, which have become increasingly assertive in pushing progressive policies at the local level.
The new law, labeled “the Death Star” by its Democratic opponents, would pre-empt a broad swath of ordinances, including those affecting labor, agriculture and natural resources. It is expected to nullify regulations such as those dealing with payday lending, puppy mills, certain sanitation requirements and other practices.
“I think the rest break ordinance is only the tip of the iceberg to what we’re going to be seeing,” said Rick Levy, the president of the Texas A.F.L.-C.I.O. “It’s probably the most sweeping transfer of power that we’ve seen in this state, transferring power from local communities to politicians in Austin.”
According to its supporters, the goal of the law, known as the Texas Regulatory Consistency Act, was to rein in a patchwork of regulations that differ by locality and could conflict with state regulation.
“For too long, progressive municipal officials and agencies have made Texas small businesses jump through contradictory and confusing hoops,” State Representative Dustin Burrows, a Republican from the Lubbock area, said in a statement when he filed the bill this year.
The law grew out of complaints about a growing number of local rules from business owners, particularly those who cross city and county lines, said Annie Spilman, the Texas state director of the National Federation of Independent Business, which lobbied for the legislation.
Ms. Spilman said the bill did not prevent employers from instituting their own rest and water break policy. She added that she was not aware of the Dallas ordinance ever being enforced.
The law does not address water breaks or other specific ordinances. Instead, it bans actions by cities to regulate work conditions that go beyond state law. Texas law does not provide for worker breaks, according to the federal Occupational Safety and Health Administration; neither does federal law.
At the moment, most cities in Texas do not require breaks either, though Austin has had an ordinance on its books for more than a decade that requires a rest break for construction workers of at least 10 minutes for every four hours worked. Dallas adopted a similar measure in 2015. The possibility of an ordinance has also been raised this year in San Antonio.
City officials in Dallas, Austin and San Antonio said they were still evaluating the potential impacts of the state law, which is broadly worded.
“The bill undermines Austin and cities across Texas in their ability to do what is best to protect people,” said Kirk Watson, the mayor of Austin, adding that he hoped contractors would “continue to uphold Austin values and continue to protect workers, especially in times like we are seeing.”
Daniela Hernandez, the state legislative coordinator for the Workers Defense Project, which works to support immigrant construction workers in Texas and backed the local break ordinances, said the new law “erodes a local government’s ability to protect its own community.”
Ms. Hernandez pointed to the state’s staggering heat wave as an indication of why a water break is necessary. “It’s only going to get worse,” she said of the triple-digit temperatures in Austin and around the state. “The heat doesn’t even end in September. Sometimes we’re wearing shorts in December.”
The ordinance in Dallas passed after the death of a 25-year-old worker, Roendy Granillo, who was installing hardwood floors in a house without air conditioning when he began to feel sick and asked for a break. The request was denied. He kept working until he collapsed.
The medical examiner’s office said the cause was heat stroke. “My parents were told his organs were cooked from the inside,” said his sister, Jasmine Granillo.
But even after several years of the ordinance being in place, some employers in the construction business in Dallas still did not know about the break requirements.
John Foster and Donny Zanger, who own Dallas General Contractor, said that they were not aware that they had to provide a 10-minute break for every four hours of work, but added that they did not need the government to tell them their employees required water.
“It’s a no-brainer,” Mr. Foster said. “I don’t know what kind of home builder would need or use that ordinance. I don’t know any builders who work their guys so much that they say, ‘OK, 10 minutes for water.’ They have access to water all day. It’s not really an issue.”
United States Representative Greg Casar, who helped lead the push for water break ordinances when he was a 21-year-old labor organizer in Austin in 2010, said he planned to start an effort at the federal level that would require water breaks on a national basis, pressing for national legislation or new administrative rules from the Biden administration.
“We are going to push every day we can,” he said.