The Construction, Forestry, Mining and Energy Union secretary is incensed that Planning and Infrastructure Minister Alannah MacTiernan has awarded Doric Constructions contracts worth about $60 million to build five railway stations.

Speaking on the eve of a national protest against Canberra's proposed industrial relations reforms which is expected to see at least 10,000 workers rally in Perth, Mr Reynolds said he had warned the WA Government that having non-unionised labour working next to workers on enterprise bargaining agreements covering the rest of the rail project was a recipe for industrial relations disaster which Ms MacTiernan would rue.

He said he had to temper his public comments so they were not used to secure court injunctions against him and the CFMEU.

However, in an ominous warning to the Government, Mr Reynolds declared: "I can tell you it's going to be a big problem for them. Undoubtedly it will be the source of industrial disputes. There will be delays and cost overruns for sure."

Mr Reynolds' threat represents the latest challenge for the Government to deliver the rail project on time and on budget. After a series of revisions, the project is now estimated to cost $1.563 billion. It rates the highest on a list of priority capital works programs being overseen by a newly established Government task force, which includes Ms MacTiernan.

Mr Reynolds said the Government's policy of awarding tenders to the lowest bidders was flawed because it resulted in inferior pay and conditions for workers.

"She (Ms MacTiernan) works on the theory, just as the rest of this Government does, that the lowest tender should always win," he said. "But the lowest tender is the company that robs the workers the most. All the unionised companies are now saying, 'Why should we pay decent wages when we miss out on all the jobs and the contractors who pay the bare minimum get rewarded with the government contracts?'."

Mr Reynolds said for that reason, construction group John Holland recently threatened to go "completely non-union".

Last week, the WA Government awarded Doric and its partner Brierty Contractors a $28 million contract to build the Rockingham and Warnbro train stations. Doric and Brierty earlier secured contracts worth $32 million for the Cockburn Central, Kwinana and Wellard stations.

Ms MacTiernan said yesterday that Doric won the contracts through an open tender process undertaken by the Public Transport Authority.

She said the Federal Workplace Relations Act had made it difficult to enforce a requirement that contractors pay award rates or have EBAs.

"Certainly we would like to be in a position to provide that level of protection for workers," she said. "However, having an EBA does not appear to guarantee industrial peace as we have seen on Packages E and F (the city and bridgeworks parts of the rail project)."

Ms MacTiernan stressed that Doric had secured government contracts worth only about $60 million from the total project budget of $1.563 billion. The vast majority of the work was being undertaken by companies with union agreements.

Doric spokesman Keith Somers said Doric had gone through an extensive tender process to win contracts the company had pitched for on a sound commercial basis.

"If it was the case that we were uncompetitive with our pay rates, then we wouldn't have people working for us," he said.

Speaking from England last night, WA Chamber of Commerce and Industry chief executive John Langoulant said the Government should always award contracts to the tender which represented the best value for money, which did not always mean the lowest bid. The issue of union membership should be irrelevant in awarding government tenders.