Tasmanian unions have rallied in Devonport outside a public hearing examining Australia's free trade agreement with China.

Federal Parliament's joint standing committee on treaties is meeting in Devonport to take submissions on the Chinese free trade deal.

Unions are angry about a clause they say will remove the need for companies to test the labour market before hiring Chinese workers on projects worth more than $150 million.

Tasmanian Greens senator Peter Whish-Wilson said it set a worrying precedent.

"We will have a parallel industrial relations system in this country for foreign workers and for Australian workers," he said.

Federal Liberal member for Braddon Brett Whiteley said the deal would not reduce incentives to train local workers.

But the Communications, Electrical and Plumbing Union said the agreement would allow Chinese employers to fly in their own workers, like electricians, carpenters and plumbers, if their investment in a project met a certain threshold.

Mr Whiteley dismissed the union's concerns.

"One of the bigger users of the 457 visa over the past few years has in fact been the union movement, which is quite ironic and quite hypocritical," he said.

"There really is a capacity there for people to bring in foreign workers, we see that now, but it's only under very extreme circumstances."