A $1.3 MILLION pay dispute involving construction workers at Bluewaters Power Station has been in the Occupational Health and Safety Tribunal in Collie this week.

WA Industrial Relations Commissioner Stephanie Mayman has been hearing from witnesses about wages lost in May.

About 900 workers were not paid about $1500 gross each after refusing to work for five days because of fly ash concerns.

Construction workers Colin Jones and Dean Lloyd gave evidence about how they were exposed to fly ash.

Between three and four more witnesses were yet to be heard as of yesterday morning, and photos were to be submitted to the tribunal.

Construction Forestry Mining Energy Union lawyer Simon Millman from the law firm Slater and Gordon said workers had a right to raise concerns about health and safety.

He said he had asked if fly ash expert Phil Ashton would be giving evidence but Griffin Coal had not replied.

Mr Millman said the commissioner would make a decision on the matter fairly quickly once all witnesses had been heard.

Management from IHI, HPT, EC and M, K and K Electrical, Essential Fire Industries, United Industries and Safe and Sound Scaffolders will give evidence in Perth in mid-November.

The hearing finishes in Collie today.

It will continue at the WA Industrial Relations Commission in Perth in mid-November.