ARRIAGA, Mexico — One of Mexico’s most powerful criminal gangs has muscled into the migrant-smuggling racket, changing what had been a relatively benign if risky industry of independent operators into a centralized business that often has deadly consequences for those who try to operate outside it.

Los Zetas, who earned a reputation for brutality by gunning down thousands of Mexicans in the ongoing battle for drug-smuggling routes to the United States, now control much of the illicit trade of moving migrant workers toward the U.S. border, experts in the trade say.

They’ve brought logistical know-how, using tractor-trailer trucks to carry ever larger loads of people and charging higher prices, as much as $30,000 per head for migrants from Asia and Africa who seek to get to the United States.

They’ve also brought an unprecedented level of intimidation and violence to the trade. Los Zetas or their allies often kidnap and hold for ransom poor migrants who try to operate outside the system. If relatives don’t wire payment, the migrants sometimes are executed and dumped in mass graves or press-ganged into jobs with the criminal group.

Nearly a year ago, Zetas gunmen were implicated in the slaughter of 72 migrants at a ranch near San […]