Union head Dave Oliver has demanded legislation to protect weekend penalty rates ''forever'' in the face of a business push for greater flexibility.

Mr Oliver, secretary of the Australian Council of Trade Unions, stepped up his call for annual leave and sick leave to transfer when people moved jobs.

Dave Oliver. Credit:Alex Ellinghausen

Business groups dismissed the ideas as complicated and costly, but the Greens offered to work with the Gillard government to beef up employment protection laws.

Workplace Relations Minister Bill Shorten said Labor had always supported penalty rates, but did not reveal whether he would adopt the call for protections to be enshrined in law.