Judge Rafael da Silva Marques ruled on Tuesday that matches scheduled to kick off between 6pm and 7:30pm (9-9:30pm GMT) could only go ahead after the referee had checked the temperature on the pitch.
Marques had already banned kick-offs between 10am and 6pm last week after several players felt ill during a match in the state's Gaucho championship that kicked off at 5pm in 40-degree heat.
"The referee must measure the temperature before the game. If it's less than 35 degrees the match can start. If it's 35, 36 or more, the referee should wait until the temperature goes down," Marques was quoted as saying on the website of the Rio Grande do Sul labour court.
"After 7:30pm, as the sun is no longer so strong, play can go ahead. I think it's a measure for workers' health and we must think about that," he added of his decision that followed a request for action from the state's players' union.
The heat has been such in Rio Grande do Sul and other Brazilian states that TV commentator and former Brazil midfielder Batista passed out before a match broadcast last week.
