The strike, which is expected to end Friday evening, threatens BHP's reputation as a reliable supplier of coal to overseas customers, the company said.

But Construction Forestry Mining and Energy Union official Andrew Vickers said workers were left with no choice as the company "did not even come close to addressing workers' claims" despite protracted negotiations.

BHP expects the industrial action to delay six ships from delivering coal to customers and affect 15 ships by the time the backlog is cleared next week.

"The strike will be extremely costly for everyone concerned - the company, the government and the 106 Hay Point employees who will lose another four days' pay, on top of the two days lost through similar action a fortnight ago," said BHP Queensland Coal president Rick Gazzard.

However, the union says it had no choice. "It's not the intention of workers to damage either BHP's or Australia's reputation, but under the legislation they are left with only three options - accept the company's offer, do nothing or take protected industrial action," said Vikers.

"The Hay Point workers chose to take action.

Gazzard said the claims were excessive when compared with other recent settlements in the coal industry, and considering the conditions already enjoyed by BHP Queensland Coal employees.

"BHP has made it clear to the unions during enterprise negotiations that the company is prepared to share with employees the benefits of the efficiencies they have helped to achieve by reaching a wages agreement which would put them near the top of their industry," he said.

"In return, we must have the same flexibility and work arrangements - including access to contractors - enjoyed by our competitors in the Queensland coal industry."