Union sources said barons were gearing up for national action which could shut down hospitals, schools and the railways after Labour made it easier to call strikes.
Party politicians and activists including a former leader have told Zack Polanski that it is in the party's interests to lend support to the Greater Manchester mayor on June 18.
Brian Booth, deputy national chairman of the Police Federation, said crime will become rife with dangerous offenders emboldened by the lack of deterrents.