MELBOURNE, AUSTRALIA - MARCH 07:  Workers walk through the city during a union organised protest against temporary worker (457) visas on March 7, 2013 in Melbourne, Australia. As Australia heads towards a Federal Election in September the row over 457 Visas is escalating, with Prime Minister Gillard vowing to tighten the guidelines, which has led Greens leader Christine Milne to accuse the PM of dog whistling.  (Photo by Robert Cianflone/Getty Images)