Sub-contractors who worked on expanding the Perth Airport say they have been left short by the problem-plagued project.

Several have spoken out, claiming they are owed hundreds of thousands of dollars in unpaid deals.

There was much excitement when the new terminal was announced over a year ago, but the project has since been smashed by cost overruns and delays.

It has led to the collapse of several companies associated with the airport expansion.

One of those to fall by the wayside was Alcom Fabrications, which entered into administration in February with over $11 million in debts.

Administrators for Alcom are investigating whether the company knowingly made false statements about its finances, which would have let it rack up debts it could not pay.

Alcom claims the project's head builder, Built Environs, owes it more than $2 million.

Meanwhile, Built Environs has launched a multi-million-dollar lawsuit against the airport authority.

The builder says the main operator is responsible for delays that have delayed the project for more than a year.

Mick Buchan from the Construction Forestry Mining and Energy Union says it is another sign there should be more regulation in the construction industry.

“The big players will just say; ‘Well take us to court now’,” Mr Buchan has told the ABC.

“There's not many construction sub-contractors that could afford the legal battles with the big end of town for chasing up those type of dollars.”

Alcom's administrators are expected to hand a report on their investigations into the company’s collapse – and the deprivation of payments to sub-contractors - to the Australian Securities and Investments Commission in coming weeks.