Thousands of London Underground drivers are set to strike on the day Jeremy Hunt announces his Budget next month.
Millions will be hit by travel chaos on March 15 after trade union Aslef has announced a walkout.
It comes after 99% of members who voted backed industrial action in a longstanding dispute over pensions and working arrangements.
Aslef members going on strike include thousands of drivers and some in management grades.
Finn Brennan, Aslef's full-time organiser on the underground said: "Our members are not prepared to put up any longer with the threats to their working conditions and pensions."
He warned that it could turn into a "protracted dispute" if Transport for London (TfL) doesn't resolve the matter.
It ramps up further pressure on a transport network which has been heavily hit by industrial action since last summer.
Mr Brennan said: "We understand that Transport for London faces financial challenges, post-pandemic, but our members are simply not prepared to pay the price for the government's failure to properly fund London's public transport system.
"Cuts to safety training have already been forced through and management is open that they plan to remove all current working agreements under the guise of "modernisation" and "flexibility" and to replace the agreed attendance and discipline policies.
"Proposals to slash pension benefits are due to be announced in the next week.
"We are always prepared to discuss and negotiate on changes, but our members want an unequivocal commitment from TfL that management will not continue to force through detrimental changes without agreement.
"Unless they are prepared to work with us, and accept that changes have to come by agreement, and bring real benefits to staff, rather than just cuts and cost savings, this will be only the first day of action in a protracted dispute."
Around 100,000 civil servants in the Public and Commercial Services union are also planning to strike on Budget day in a long running dispute over jobs, pay and pensions.
