Boris Johnson was accused of failing to lift a finger to prevent the rail strikes which have caused travel chaos.
Labour leader Sir Keir Starmer said the Prime Minister and Transport Secretary Grant Shapps had refused to meet the unions representing rail workers ahead of this week’s industrial action.
But the Prime Minister hit out at Sir Keir, saying it was a “disgrace” that Labour MPs had joined RMT members on the picket lines outside railway stations.
“What we have got to do is modernise our railways,” Mr Johnson told the Labour leader.
Mr Johnson said Labour was “backing the strikers while we back the strivers”.
Sir Keir shot back: “The Prime Minister of this country and his Transport Secretary haven’t attended a single meeting, held a conversation or lifted a finger to stop these strikes.”
But he said on Monday they found time to attend a “lavish ball” to raise funds for the Tory party, where a donor has £120,000 to have a joint dinner with Mr Johnson and predecessors Theresa May and David Cameron.
“If there is money coming his way, he is there,” Sir Keir said.
The Prime Minister said: “We are doing everything we can to prevent these strikes.”
But it was for the rail companies and the unions to negotiate a settlement, he said.
Following Tuesday’s strikes on the rail network and London Underground, trains will also be halted on Thursday and Saturday.
Labour’s frontbenchers had been told to avoid picket lines but senior party figures including whip Navendu Mishra joined striking rail workers.
Sir Keir is understood to be waiting until the end of the industrial action before instructing chief whip Alan Campbell to deal with any disciplinary issues relating to the strike.
Following PMQs, a Labour spokesman said Mr Campbell would make a decision in the “next few days”.
He would not be drawn on what form any action might take, but said “the chief whip is aware of Keir’s wishes”.
“I think the right way is for the process to go ahead as it should, and that is for the chief whip to speak to the individuals concerned,” he added.