Running a racing stable without foreign workers is an impossibility for most Australian trainers.

Of the 20 track riders on the work roster at Sydney's leading stable on Thursday, 16 are from overseas, mostly England and Ireland.

Trainer Chris Waller is one of many who fear the repercussions of reforms to the 457 visas many foreign workers use.

As the prime minister argues it is about keeping jobs for Australians, the types of jobs that need filling in the racing industry are those Australians don't want or are not qualified to perform.

Most Sydney stables start work at 4am, and Waller is an advocate for delaying that by a couple of hours.

Waller's racing manager Charlie Duckworth is about to get residency in Australia after first learning his craft in his native England where the starting times are more civilised.

"No-one wants to work the early hours," Duckworth said.

"If there is no 457 visa there is no incentive to stay. It is a nightmare for employers."

Randwick trainer Anthony Cummings, who is in partnership with his son Edward, says around 80 per cent of the stable's workforce is from overseas, also mostly from England and Ireland where the training in thoroughbreds is superior.

"Sometimes they will come on six month visas and then we will offer sponsorship," he said.

"The people who come here are of a high quality and have the necessary qualifications to deal with thoroughbreds.

"There is nowhere here where people can get trained to that standard.

"My experiences of those who come from TAFE has not been fantastic. They are not equipped to deal with thoroughbreds.

"In the old days they would come off farms with horse skills but now they use helicopters and motorbikes for mustering and the horsemanship isn't there.

"We have 30 staff and if we didn't have foreign workers there would be me, Edward and about three others."

As Waller advocates for later starting times, Cummings puts it into practice and says it should be the norm.

"If we want to gallop horses on the grass then they have to go in the dark," Cummings said.

"That is something that is forced on us and not something they do in England where they start at sun-up.

"But if they are going on the dirt track then we wait until after it is re-laid between 6.15 and 6.40.

"There is a push from trainers for later starting times but I've been doing it for 20 years.

"It's about providing the best surface for the horses and the best environment.

"Working in the dark doesn't help the horses. It was introduced a long time ago to try to beat the bookies and has become cemented in place.

"It's not good for the horses. It's not good for anyone."