The Manchester mayor said the prime minister had only performed “half a U-turn”, which did not go far enough.
His comments, at an event at the Glastonbury festival, will be seen as a direct challenge to the PM’s authority.
The government announced on Friday that it was watering down its plans to cut £5 billion from the welfare budget after a rebellion by more than 120 Labour MPs.
It means that those currently in receipt of personal independence payments (PIP) and universal credit will not be affected, but those claiming in the future will receive less cash.
Starmer hopes the concessions will be enough to persuade Labour MPs to vote for the government’s reforms in the Commons on Tuesday.
But Burnham said: “What’s been announced is half a U-turn, a 50% U-turn. In my view I’d still hope MPs vote against the whole bill when it comes before parliament.”
He said Labour MPs “face the prospect, if they accept this package, someone could come to their surgery in two years saying ‘why did you vote to make me £6,000 worse off than someone exactly the same, but who was protected because they were an existing claimant’?”
“I hope they think carefully before the vote, because the vote will create that unfairness and divide in disabled people,” he added.
