'Illegal' migrant contracts: union

A large construction company is accused of stopping at least 11 Melbourne-based skilled migrants from joining a union.

The Electrical Trades Union has called for a senate review of the `rotten' 457 guest worker system, accusing Thiess of putting `illegal clauses' in contracts allowing migrant workers to be sacked and deported if they joined a union.

ETU assistant national secretary Dave Mier said the case showed the risks of allowing large companies to `self-regulate' the visas.

"It's time for an immediate review of all 457 employment contracts from companies given self-regulation powers to see how rotten this system is," he said on Monday.