Workers in the United Kingdom's capital city were breathing a sigh of relief on Monday when London Underground train drivers called off a planned strike that looked set to paralyze the transit system for four days.

The strikes had been set for Tuesday, Wednesday, Thursday, and Friday and were expected to massively disrupt the system that handles more than 4 million trips a day, forcing people to walk, cycle, bus, or try to get a cab in massively overcrowded conditions.

The Rail, Maritime and Transport, or RMT, union had called for the strikes in response to the employers' plan to introduce a four-day working week featuring condensed hours.

The union was understood to be especially angry that the change would mean workers got four paid lunch breaks instead of five.

The employer, Transport for London, or TfL — which is owned and operated by the Greater London Authority, the municipality that runs the city — had insisted the change was in the interest of improving employees' work-life balance. It said drivers were free to opt out of the four-day week and continue to work a five-day week instead.

While the condensed four-day working week had been vehemently opposed by the RMT union, the other big union representing train drivers in the UK capital, Aslef, said earlier that it was "exactly the sort of deal every trade union should be trying to achieve" and that its drivers would be working as usual throughout the RMT strike.

Aslef said the condensed working week would mean drivers got an extra 35 days off each year "in return for some fairly minor changes to working conditions".

"It will be the first strike in the history of the trade union movement designed to stop people having a shorter working week and more time off," an Aslef spokesperson said before the RMT strike was canceled.

An RMT union spokesperson said on Monday afternoon as the strike was canceled: "At the 11th hour, the employer has shifted its position allowing us to further explore our members' concerns around the imposition of new rosters, fatigue, and safety issues.

"The dispute is not over and more strike action will follow if we fail to make sufficient progress."

The RMT said additional strikes on June 16 and June 18 have been called off, but that there will now be new strikes on the London Underground system on June 2 and June 4 if the dispute remains unresolved at that time.

Nick Dent, director of customer operations for London Underground, told the BBC: "We are pleased that RMT has withdrawn its planned industrial action this week.

"Our proposal for a voluntary four-day week is designed to improve both work-life balance for drivers and the reliability of service for customers.

"We look forward to further discussions on the implementation of these proposals with all of our trade unions."