Railway control room workers in Brighton could bring the main line and coastway lines to a halt when they go on strike later this month.
The workers are members of Unite which said that its members employed by Network Rail would join other rail unions in taking action on Thursday 18 August and Saturday 20 August.
The Transport Salaried Staffs Association (TSSA) also said that thousands of its members at Network Rail would strike on the same dates.
Unite said that the electric control room operatives played a crucial role because they were responsible for managing and controlling the power supply to the rail network.
The workers are based at the control rooms in Brighton, Selhurst and Raynes Park, in London, Paddock Wood, in Kent, Romford, in Essex, and York.
Unite general secretary Sharon Graham said: “Our members played a crucial role in keeping the rail network functioning throughout the pandemic, ensuring that essential workers and goods could be transported.
“The thanks they get for their sacrifices from their employers is a derisory offer that amounts to a kick in the teeth.
“Unite is entirely dedicated to defending the jobs, pay and conditions of its members.
“Our members at Network Rail will receive the union’s total support until this dispute is resolved and the workers receive a fair pay deal.”
Unite said that their members had not received a pay rise for three years and were increasingly struggling to make ends meet because of the ‘cost of living’ crisis.
Unite national officer Harish Patel said: “Strike action by Unite members will undoubtedly cause further disruption to the rail service but this dispute is entirely of Network Rail’s own making.
“Our members expect and deserve a pay rise which tackles the ‘cost of living’ crisis that faces them.”
The TSSA said that it served notice after asking Network Rail asked for “clear assurances and clarity” on job security and working practices.
No such assurances were forthcoming, the union said, and the 14 days’ notice of strike action, required by law, had now been given.
The Rail, Maritime and Transport (RMT) union has already said that its members would strike on Thursday 18 August and Saturday 20 August.
And RMT members on London Underground will stage a 24-hour walkout on Friday 19 August.
Members of the drivers’ union ASLEF will strike at nine train companies on Saturday 13 August after industrial action last month.
Network Rail’s lead negotiator Tim Shoveller said: “We are doing everything we can to avoid disruption for our passengers later this month but it appears that our unions are co-ordinating their strike action to maximise impact.
“We urge all our unions to work with us to agree a deal that is fair for their members – our employees – and affordable for taxpayers and passengers, and we think it’s only right that members have a say on the offers we’ve made.”