Workers from China and the Philippines who have traveled to Australia to work under the 457 visa program have been forced to sign illegal contracts barring them from a wide range of religious and political activities, including joining unions. While the contracts seem to be issued in the workers' country of origin, their clauses are being enforced in Australia, leaving many of the workers struggling to find some sort of legal recourse.
See "Migrant workers facing dismissal for joining unions", Nick O'Malley and Michael Bachelard, October 8, 2006