A meeting between the workers and representatives from the Construction, Forestry, Mining and Energy Union on Tuesday was told the matter was more complicated than first believed.

Manildra and Chia Tung - the Taiwanese-based company that contracted the work - were invited to attend the meeting but did not turn up.

"It seems that more than one company was involved in employing the workers, and they in turn answered either to Chia Tung or yet another company in between," CFMEU state secretary Brian Parker said after the meeting.

"This brings into question whether or not the workers are properly insured for workers' compensation."

Mr Parker said the workers had indicated they were part of a national network that might reach into Queensland, Victoria and Western Australia, as well as other parts of NSW.

"Manildra cannot wash its hands of this mess. Workers talked to management about what was happening here. They cannot simply claim they have no formal responsibility," Mr Parker said.

"The government needs to investigate every part of the Manildra Group, the Chia Tung Development Corporation, and every subcontractor and migration agent involved. There's a huge racket going on here. It's like a series of nested pyramids, one company inside the other."

One of the Filipino workers, Percival Mapano, said that under his contract, he could be transferred to other sites in the country.

"I am sad Chia Tung is taking our rights from us," he said.

Mr Parker said he hoped the fact that Manildra had donated $285,604 to the Liberal Party over the last two years did not prevent Immigration Minister Peter Dutton from stamping out what he said amounted to modern day slavery.

"The CFMEU is working closely with all the overseas workers at Bomaderry to recover all of their entitlements and ensure their employment and visa status is protected."