Strikes by drivers on London Underground next week will go ahead, the RMT union has announced, paving the way for more days of transport disruption.

Two 24-hour stoppages are to take place, from 00.01 to 23.59 on Tuesday 2 June and Thursday 4 June, because of differences over a planned four-day week.

An RMT spokesperson said: “Strike action by London Underground drivers next week is scheduled to go ahead following TfL’s continued refusal to engage meaningfully with the union’s concerns over the proposed compressed four-day working arrangements.

“Our members have raised serious concerns around fatigue, longer shifts, reduced flexibility and the impact these proposals could have in a safety-critical role.”

Transport for London said it expected services on most tube lines during the strike, but has told commuters to expect disruption. It added that other services including the Elizabeth line, London Overground, DLR and tram would run as scheduled, but would be busier than normal.

TfL has said its proposals for a four-day week would be trialled on a voluntary basis. Its proposal has been endorsed by the Aslef union, which represents a slight majority of tube drivers.

Claire Mann, the chief operating officer at TfL, said it was disappointed that the RMT was continuing its industrial action.

“We still believe that the points they have raised can be worked out in time, through more detailed discussions and we are continuing to talk to the union’s representatives to find a way to avoid disruption to London,” she said.

She urged the RMT to work with TfL to resolve the dispute, adding: “A significant number of drivers have indicated that they want us to progress plans for the pilot of this new working pattern on the Bakerloo line, bringing benefits both for our colleagues and our customers.”

The RMT’s opposition to London Underground plans for a voluntary four-day week has already led to industrial action, most recently in April.

Hopes were raised that differences between the two sides may soon be resolved when the RMT called off at the last minute a two-day strike planned for mid-May.

However, at the same time the union also moved forward further strikes planned for 16 and 18 June to 2 and 4 June, saying the dispute was not over and that it was prepared to take more industrial action if the two sides failed to make sufficient progress.

The RMT said it remained “available for meaningful talks” with TfL, but cautioned London Underground against carrying out what it called a change to drivers’ working conditions “while refusing to properly address legitimate safety and workplace concerns”.

Previous waves of industrial action by the RMT over the four-day week proposals had found little public sympathy and had also mystified Aslef, which felt the proposal presented a significant improvement in working conditions for tube drivers.