The Australian Council of Trade Unions fears a push by major retailers to exempt senior staff from weekend rates and overtime could form a precedent for other industries, and has called for political parties to commit to protecting penalty rates.

Coles, Woolworths, Kmart and Costco have united with other retail chains like 7-Eleven, T2 and Mecca to back an Australian Retailers Association application to the Fair Work Commission to relax rules on rostering, breaks and other minimum conditions in the retail industry award.