In a press conference, Mick Lynch said the Labour leadership needed to find a way to connect with working-class people.
He also warned that the UK could see a “wave of industrial action”.
Asked by the PA news agency if he felt supported by the Labour leadership, he said: “Well, the Labour leadership have got a problem, haven’t they?
“They’re against workers being exploited, and they’re against this Tory Government.
“They’ve got to find a way to connect to working-class people in working-class communities so they can get their votes back.
“They’ve got to find their message. They’ve got to find some policies that get back to where working people are.”
Mr Lynch said that it was up to Labour to ride the wave of industrial action and connect with it.
“We saw many working people out on the streets on Saturday. I think there’s going to be more of that. And I think there’s going to be a wave of industrial action, a wave of ballots, and a wave of campaigning.
“So Keir Starmer and his team have got to work a way how they can connect with that and how they can ride that wave of resistance and are in harmony with it.”
Mr Starmer has said he does not want the strikes, which are the largest in a generation, to go ahead.
“My position and the Labour Party position is that I do not want these strikes to go ahead”, the Labour leader said on Saturday.
“I want all the parties around the negotiating table, even at this late hour, to resolve this.
“But, like the British public, I’m frustrated because the Government is sitting it out, it’s not lifting a finger to resolve these strikes.”