Keir Starmer has branded Rishi Sunak "pathetic" for attempting to blame Labour for mass strikes - after 13 years of Tory rule.
The remarks come as up to half a million people take part in strike action - the biggest industrial action the country has seen in over a decade.
Members of seven trade unions walked out on Wednesday, affecting universities, trains, and dozens of Government departments.
Teachers in England and Wales, who are members of the National Education Union (NEU), also embarked on their first day of strikes, disrupting thousands of schools.
Speaking at Prime Minister's Questions, Mr Sunak highlighted Labour's decision to vote against draconian anti-strike laws on Monday.
He added: "He voted with Just Stop Oil to water down the Public Order Bill and what do the unions and Just Stop Oil have in common? They bankroll him and his party."
He also accused the Labour leader of siding with "extremist protestors and union bosses" as he dodged questions over sleaze in the Tory ranks.
But Mr Starmer replied: "After 13 years in power trying to blame the Labour Party for his failure to sort out the strikes, it's rank pathetic."
As the exchange took place, the Trades Union Congress held a series of protests against the Government's plans for a new law on minimum service levels during days of industrial action.
On Wednesday the General Secretary of the TUC Paul Nowak also warned the Prime Minister to expect a further wave of strikes as industrial disputes "won't magically disappear".
Speaking in Westminster, he said: "There isn't a single public sector worker who is taking industrial action today that wants to be on strike.
"They are losing pay, they are not being able to deliver the services they are proud to deliver to the public.
"But the responsibility for these strikes lies firmly with the Government. It's been months now and still the Government hasn't sat down and seriously talked about a real pay rise for our public sector workers.
"It really is now the responsibility of Rishi Sunak and Jeremy Hunt to get round the table and make sure the resources are available to fund decent pay in our public services."
As well as the impact on inflation, the Government must consider the wider affordability for UK taxpayers of potential pay rises for public sector workers, No10 later said.
The Prime Minister's official spokesman said: "I think it's important for the public to understand that when unions understandably want more pay for their members, the Government has to consider how those things are paid for, and across the board there are three main ways to do that, there are tax rises, there are borrowing and there are cuts.
"And it's those kind of considerations that a Government, a responsible Government, needs to consider."
