LOUISVILLE, Ky. (AP) — The backside of Churchill Downs hums with activity as workers clean stalls, bathe horses and lead the muscular animals on strolls to cool them down after workouts. The quiet is broken when they speak to each other and the horses – in Spanish.

Though they do their work a world away from the grandstand and Millionaire’s Row, where fans will sip mint juleps, don fancy hats and cheer for their Kentucky Derby favorites on the first Saturday in May, immigrants have become indispensable at Churchill Downs and other tracks, people in the industry say. Now, fear is spreading that a Trump administration crackdown on immigration will be a calamity both for the tracks and for many of their workers.

While there’s widespread acknowledgement that some jobs go to undocumented workers, many trainers rely on the H-2B visa program to supply immigrant workers legally, and the tightening of that program has contributed to a worker shortage.

Some argue that the presence of foreign workers has a downward drag on everybody else’s income. But Dale Romans, the second-winningest trainer in Churchill’s history, says he can’t find American workers to do the jobs.

“This is definitely a business that survives on an immigrant workforce,” Romans said. “Without it, I don’t know what we would do.”

The apprehension on the backside has been stoked by the election of Donald Trump, who staked out a role as an immigration hard-liner during the campaign and referred to some Mexican immigrants as rapists and murderers.

“I wouldn’t say it’s an extreme fear, but there is nervousness” among Churchill’s immigrant workers, track chaplain Joseph del Rosario said. “There’s fear they’re going to get kicked out just because they’re not citizens.”

Said one 53-year-old backside hand who has worked at racetracks across the country: “I’m scared. Because one day, I don’t know, they catch me and send me to Mexico.”

The man, who agreed to an interview only on the condition his name not be used because he fears being exposed to immigration authorities, said his visa expired a couple of years ago but he has kept working, moving up the ranks in the barns where he works. His family has made a life in the United States; if he had to return to Mexico, he said, he’d probably toil in the avocado fields.

Even workers here legally on visas worry about the threat of immigration crackdowns.

“A lot of people here, they’re scared,” said Cesar Abrego, a 46-year-old groom who came from Guatemala on an H-2B visa. “With the president coming, everybody says, ‘Be careful.'”

Like many of the immigrant workers, Abrego dutifully sends money back home. He has three children to support, and worries the visa program that sustains his family will be cut. He could find construction or roofing work in Guatemala, but believes his approximately $450-per-week take-home pay as a groom would be cut more than half.

It’s a complicated, time-consuming process for horsemen to get visa workers to their barns. Trainers typically hire immigration attorneys to handle the paperwork.

The H-2B program is capped at 66,000 visas per year, and horse racing competes with many other industries for the coveted slots. Applications for the visas far outpace available slots. The crunch worsened when the program’s “returning worker” exemption expired last September.

Congress has not reauthorized the exemption, which allowed existing H-2B visa holders to keep returning on the same visas, which weren’t counted against the cap. Immigration lawyers and members of horsemen’s groups have been meeting with lawmakers in hopes of getting the exemption reinstated.

“The shortage of workers on the backside is severe,” said Will Velie, an Oklahoma-based immigration attorney. Trainers unable to secure enough H-2B workers “have a choice between turning away work or breaking the law if they can find people that are here undocumented.”

At Barn 4 on the backside of Churchill, Romans’ crew was down about 15 workers for the spring racing season at Keeneland in nearby Lexington, as the trainer prepared for the upcoming meet at Churchill. Romans’ latest Kentucky Derby contender is J Boys Echo, winner of the Gotham Stakes at Aqueduct.

The staffing shortage was more dire for trainer Gary Patrick, who races mostly at tracks in Indiana and Florida. The 70-year-old Patrick had to wield a pitchfork to clean 20 stalls each morning as he waited for visas to be approved for more immigrant workers he wanted to hire.