Keir Starmer has pledged to repeal any anti-strike legislation brought in by the government should Labour win the next election.
Rishi Sunak is reportedly set to announce new laws which will allow employers to sue unions and sack staff in an effort to curb the right to strike.
Taking questions in east London following a speech on Thursday, Starmer said he would reverse such a move as it would “make a bad situation worse”.
“Obviously we will look at what they bring forward, but if it is further restrictions then we would repeal it,” the Labour leader said.
“The reason for that is I do not think that legislation is the way that you bring an end to industrial disputes.”
According to The Times, the prime minister could announce new laws to require “minimum service levels” in six sectors, including the health service, rail, education, fire and border security.
It comes amid widespread industrial action across the public sector including on the railways and in the NHS.
Earlier, Mick Whelan, the general secretary of Aslef, said unions could take legal action against any new crackdown on the right to strike.
“We’re currently with 11 other trade unions taking legal action against the last set of laws they put in place and we would look at doing that in future as well,” he told Sky News.
Rail passengers face a third consecutive day of travel disruption today because of a strike by train drivers, represented by Aslef.
RMT general secretary Mick Lynch has warned that industrial action will need to continue beyond May unless a reasonable offer is made to the union.
New TUC leader Paul Nowak has written to the prime minister calling for an urgent meeting to discuss the industrial disputes, saying ministers should open pay negotiations with unions.