Cleaners on the Hitachi/Great Western Railway contract staged a solid 48-hour strike on Tuesday and Wednesday last week.
Strikers are employed by outsourcing giant ISS and are based at the North Pole Depot in west London.
The RMT members are striking against changes to shift patterns that would wreck their work-life balance.
Report highlights dangers on the tracks
The RMT union has called for an absolute ban on contracting out after a shocking report into the death of a track worker.
It found that the man killed by a passenger train in south London was on a zero hours contract, probably fatigued, and exposed to danger.
Safety inspectors demanded that Network Rail reviews its outsourced labour suppliers.
The Rail Accident Investigation Branch (RAIB) report said the man had been placing equipment on the track at Stoats Nest Junction, near Purley, last autumn.
He was walking with his back to the train, which was travelling at about 69 mph.
RMT general secretary Mick Cash said, “Once again the RAIB has criticised safety standards for the protection of track workers.
“This latest report should force real change across the industry right now.
“Warningafter warning from this trade union on fatigue, zero hours and casualisation has not being properly addressed by Network Rail or the safety regulator.
“For all the talk of a modern, digital railway those in charge can’t even guarantee basic levels of safety for track workers.”
Two track workers were killed at the beginning of this month in South Wales.
Heathrow Airport could grind to a halt this summer as 4,000 workers threaten strikes.
Workers across the airport’s five terminals are set to walkout for six days in July and August.
They are set to strike after rejecting a 2.7 percent 18month pay offer.
Their Unite union says it works out to just £3.75 a day extra for the lowest paid workers.
Workers are furious about their poverty pay while Heathrow chief executive pocketed £4.2 million in basic pay in 2018.
Unite officer Wayne King, said, “We will not allow Heathrow bosses to get away with low pay.”
“All our members are seeking is a pay deal which recognises their important role in keeping passengers safe and on the move, in addition to a commitment by Heathrow bosses to close pay disparities which are leading to a high turnover of staff.”
Workers are set to strike on Friday and Saturday of next week, as well as on 5, 6, 23 and 24 August.
Some 43 Unite union members at Stansted Airport in Essex are set to walk out for 17 days across July and August.
The check-in workers are employed by Stobart Aviation Services.
Bosses are refusing to pay wages in line with other workers doing similar jobs.
Workers are also fighting a comprehensive breakdown in industrial relations and for union recognition.
They are set to strike on Thursday of next week, 29 July and for 15 days in August.
Two groups of workers at Gatwick Airport are balloting for strikes.
Some 100 Unite union members who scan luggage for explosive material and other dangerous items are fighting for a 50p increase to their £8.50 hourly rate.
Facilities workers employed by outsourcing giant ISS, also members of Unite, are also fighting for better pay.
Management have reneged on a previous offer of an increase in April 2019. The ballots end on 26 July.