A senate inquiry into road safety heard from the Transport Workers' Union on Thursday that unreasonable demands by major businesses should be held to account over crashes.

The TWU claims trucking is the country's deadliest profession, with truckers 15 times more likely to die than any other profession. The union claims 46 per cent of drivers in the Coles supply chain felt pressured to skip breaks, 28 per cent felt pressured to speed and 26 per cent felt pressured to carry overweight loads.

Nick McIntosh, secretary of the TWU's South Coast and Southern sub-branch, said retailers had to shoulder blame and kickstart safety reforms.

"The top of the supply chain is the issue. They control everything, they set the contracts, they say how much they're willing to pay and the trucking company has to make it work, otherwise they go to a lower bidder," he said.

"They contract it out multiple times, so the margin left for the driver isn't even enough to pay himself an income without staying on the road for excessive hours, or skipping safety measures.

"The big end of town says take it or leave it."

Mr McIntosh said drivers in the Illawarra and throughout the country were forced to skip breaks or drive dangerously long hours to earn more money, or forego necessary safety maintenance to save money.

"It happens every day [in the Illawarra]," he said.

"Big companies contract out and say it's not their problem, but that's rubbish. That's what is killing the industry."

The Senate inquiry will report its findings in September.