Andy Burnham has said Labour shouldn't "fall into the trap" criticise striking rail staff and accused the Tories of trying to "demonise" struggling workers.
The Greater Manchester Mayor weighed in on next week's mass strike action, saying it was "entirely their right" for RMT members to walk out in a dispute over pay and redundancies.
He accused the Government of wanting to stoke controversy over the industrial action - but said Labour should be on the side of workers struggling with the cost of living crisis.
Mr Burnham, who has refused to rule out another leadership bid, also told Keir Starmer that the party needed to spell out what it stands for.
His comments came as union-bashing Tories tried to blame the strikes on Labour - despite it emerging that ministers have failed to meet rail workers leaders since March.
In a desperate attempt to shift responsibility, Health Secretary Sajid Javid wrote to his opposition number Wes Streeting to accuse him of backing the strikes.
But Mr Streeting hit back, saying: "It looks like you confused me for [Transport Secretary] Grant Shapps - the person who could prevent these strikes."
Mr Burnham was asked about the strikes on Thursday as he set out new plans to cap bus fares in Manchester.
Asked whose side he was on, he told the BBC's PM programme: "I will never be the kind of politician that criticises anybody for fighting for their income, for their family, to pay the rent.
"It’s entirely their right in difficult times to do that."
Mr Burnham accused the Tories of trying to "demonise workers" rather than fixing the issue.
"There’s a thought in my mind that they actually want these strikes, like they wanted the controversy about the Rwanda plane,” he said.
"I don’t think Labour politicians should fall into the trap of criticising workers that are fighting for their incomes in the middle of a cost of living crisis.
"Everybody should turn their fire on the people who can fix this and that's the Government."
He also urged Mr Starmer to be clearer on the party's vision, as the Labour leader was hit by anonymous negative briefings that he is too dull.
“There can’t be much further delay now in saying ‘This is what we are about’ so that people can then get the sense of where the next Labour government would go,” Mr Burnham said.
"That really does have to happen at the annual conference in Liverpool. I would have said it should have started more last year but people will take different views about that.
"The platform has been built, the foundations have been shored and now is the moment to say you can see this Government and this is what we will be doing differently."
London Mayor Sadiq Khan also accused the Government of "inciting" next week's Tube strike and said ministers were "whipping up" division with the Transport for London funding deal.
He said: "At the core of this is the Government... orchestrating and engineering and inciting a strike in London by attaching these conditions to the funding deal, which has got the trade unions really concerned.
"The Tories are in Government and this is classic deflecting from Shapps and Johnson who are responsible for this divisive politics, for whipping up them versus us, communities versus workers.
"And now they've got the audacity to blame Her Majesty's Official Opposition for these strikes when it's the Government that's in the cockpit.
"It's punishing the wrong people - it's the Government who are attaching these strings, not Londoners, not our businesses, not our key workers."
Mr Starmer clashed with Boris Johnson over the strikes at PMQs on Wednesday.
He told the PM: "I don't want the strikes to go ahead. He does so he can feed on the division."
