A rail dispute could hit Midland Mainline (MML) travellers going to the Live8 event in London on 2 July as a union announces more industrial action.
The strike could hit travellers to major events
The latest RMT strike day will coincide with the Hyde Park concert, Wimbledon ladies' tennis final, Gay Pride and the NatWest cricket final at Lords.
MML runs 130 daily services from London St Pancras to Sheffield, through Beds, Northants, Notts, Derbys, and Leics.
Friday was to have seen the last of four 24-hour stoppages in a safety row.
A dozen MML services have been cancelled on Friday - and another 12 are partly affected, seeing some trains missing out the final legs to Sheffield, Leeds and Burton-on-Trent.
Virgin Cross Country will accept MML tickets between Leeds, Sheffield and Birmingham New Street. Northern and Thameslink will be accepting MML tickets on their networks.
Action on the last three Fridays saw a halving of trains from to and from the East Midlands, and virtually no through trains to Yorkshire.
Derby-based MML has been able to run more services on each consecutive strike day, but the union has since announced plans to ballot more staff and step up action.
The RMT strike aims to highlight safety issues. The union's Ken Usher said they had come close to settling the dispute but had not had the assurances they needed.
MML said it had not been formally told of the new strike date.