Union phone calls insult voters: Robb

Unions are "insulting" the voters of Canning by funding robocalls to raise concerns about the China free trade agreement, says Trade Minister Andrew Robb.

A by-election is being held in the West Australian seat on Saturday, with concerns about the trade deal featuring heavily in Labor and union campaigning.

Mr Robb told parliament Canning voters had been the subject of "deceitful" automated phone calls and Labor should distance itself from the misinformation.