TUC president Matt Wrack said the party must stop being "overly-managerial" if it wants to inspire voters.
The TSSA union was engulfed by accusations of sexual harassment and bullying.
February 1 will see the most public sector walk-outs yet.
Around 100,000 workers will walk out of 126 employer areas in protest over pay and pensions.
The Trades Union Congress tells its members to prepare for legislation to be published when parliament returns.
The unions have been thrown into the spotlight as workers strike over rampant inflation and the worst economic crisis in decades.
Walkouts also mooted at the Royal Mail after the recent rail strikes.
As the UK’s three biggest unions prepare to change leaders, what will it mean for their members and for Labour?
Bosses are telling staff "sign up to a new contract which is worse or you’re out", says union boss Frances O'Grady.
NEU surge is part of wider spike in trade union activism as workers seek better health and job protection