London’s underground network is expected to be affected over four days this August as the Rail, Maritime and Transport (RMT) union calls for two 24-hour strikes from August 25.

The RMT is asking all London Underground members (excluding train drivers and instructor operators) to strike for 24 hours between 6.30pm on Tuesday, August 25 and 6.30pm on Wednesday, August 26 then for another 24 hours at the same time on Thursday, August 27, taking the action through to 6.30pm on Friday, August 28.

The union is also appealing to train drivers and instructor operators to walk out for the same amount of time starting and finishing slightly later – at 9pm on those days.

This means services will be disrupted for four days straight, with a normal service potentially running Tuesday morning and Thursday morning only.

In a letter on the RMT’s website, general secretary Mike Cash said: “You and your colleagues have already taken part in two separate 24-hour strikes, and other forms of on-going industrial action, which have been solidly supported and meant no London Underground services ran on Thursday, July 9, or Thursday, August 6 .

“Following a number of resolutions received from RMT Branches, your reps met at Unity House to discuss an escalation of the action, including a possible 48-hour strike.

“As before, this action is also in conjunction with members in other Unions.

“The previous strike action has promoted further discussions to take place at Acas over this dispute but as you are aware, LUL has not table a proposal that would meet members’ demands over pay and night running and as a result, the decision has been taken to call you out for a longer period.”

ASLEF has told IBTimes it will not be taking part in the strikes.

A spokesman told the publication: “We are still negotiating, we are back at Acas tomorrow and we are optimistic that a deal can be done.”

London Underground's chief operating officer Steve Griffiths said: "Our customers and London’s businesses want to see this dispute resolved and we call on the unions to engage in calm and realistic discussion with us to achieve that.

"Yesterday, however, and having previously argued that it was ‘not about money’, the RMT leadership made further demands for unaffordable pay rises and the hiring of even more staff – including the reversal of the modernisation of customer service in LU stations. They expect our customers to pick up a bill running into hundreds of millions of pounds for this through higher fares or by forcing us to cut back investment to improve Tube services in a rapidly growing city. No responsible management can give in to such demands.

"Instead of yet more strike threats, we need level headed and sensible discussion on how to deliver a modern transport service for London, alongside fairly rewarding our hardworking staff and protecting their work-life balance. That deal needs to be affordable and sustainable – and certainly not be at the expense of massive fares rises or cuts to Tube improvements – and can only be agreed around a negotiating table, not through strike threats. We remain ready at all times to meet and negotiate such an agreement for the benefit of our staff, customers and London as a whole. We urge the unions to join us."