Unions will marshal thousands of activists to shore up the blue-collar vote in dozens of at-risk regional and outer-suburban seats to keep Labor in government and defend industrial relations changes that have given workers more power.

At an ACTU campaign meeting last month, secretary Sally McManus said the campaign would be a defensive one to protect the gains won during the Albanese government’s term, according to union sources speaking on the condition of anonymity because they were not authorised to speak publicly.