Thousands more workers at Network Rail are to be balloted for strikes in escalating disputes over pay, jobs and conditions, the TSSA union announced.
It comes amid warnings of a "summer of discontent", with rail workers poised for the largest walkout in more than 20 years.
If members opt to strike, it could see action taken toward the end of July - and will follow widespread strikes across the sector, with separate walkouts planned this month.
Today it was confirmed that the Transport Salaried Staffs Association (TSSA) has served notice to ballot more than 6,000 staff at Network Rail (NR) in a dispute over pay, conditions and job security.
The TSSA has previously announced strike ballots among its members at four rail companies - Avanti West Coast, CrossCountry, East Midlands and West Midlands Trains - while members of the drivers union Aslef are also striking later this month at Hull Trains, Greater Anglia and Croydon Tramlink.
Members are being asked to cast two votes: one on strike action and another on action short of a strike.
The ballot opens on June 20 and closes on July 11.
In the event of a yes vote, strike action could be held from July 25.
Members of the Rail, Maritime and Transport union (RMT) at Network Rail and 13 train operators will walk out on June 21, 23 and 25.
The RMT also announced another 24-hour strike on London Underground in a separate row over jobs and pensions.
Tube workers will strike on June 21 to coincide with the first rail strike, threatening widespread travel chaos.
Tory plans to break strikes on the railways by hiring agency workers instead have been blasted by the recruitment industry, unions and Labour.
Shadow Chancellor Rachel Reeves warned the radical crackdown - designed to ensure there are enough workers to keep trains running during a walkout - would be unsafe.
And unions warned the move would be “reckless”, with PCS union general secretary Mark Serwotka said it would be an “outrageous act” that would “undermine” disputes and lead to “bitterness and division”.
Neil Carberry, Chief Executive of the REC which represents UK recruitment agencies, said: “Repealing the ban on agency workers replacing workers who are on strike is the wrong policy. It puts agency staff and agencies in a completely unfair position.”
It came after reports Transport Secretary Grant Shapps could change the law - after a set of planned walkouts this month - to allow agency workers to fill the gaps left by striking workers.
Asked about the proposal, Cabinet minister Brandon Lewis said the government was "not taking anything off the table”.
Members of Aslef on Hull Trains will strike on June 26, at Greater Anglia on June 23 and on Croydon Tramlink on June 28 and 29 and July 13 and 14.
The TSSA said it will ballot hundreds of workers for industrial action at train operator Avanti West Coast in a dispute over pay, conditions and job security.
Members of the Rail, Maritime and Transport (RMT) union are set to strike on Network Rail and 13 train companies later this month, while the RMT and Unite have announced a walkout on London Underground as well.
TSSA said it is demanding from Avanti a guarantee of no compulsory redundancies for 2022, no unagreed changes to terms and conditions, and a pay increase which reflects the rising cost of living.
Voting will start on June 15 and close two weeks later, with the union saying strikes could start in mid-July if there is support from members.
TSSA general secretary Manuel Cortes said: "Avanti West Coast needs to come to the table to face the concerns of their staff and tell their paymasters in government that widespread rail disruption is on the cards.
"Avanti West Coast staff are asking for some basic fair treatment - not to be sacked from their jobs; a fair pay rise in the face of a cost-of-living-crisis; and no race to the bottom on terms and conditions.
"We could be seeing a summer of discontent across our railways. We are preparing for all options, including co-ordinated strike action."
Avanti operates passenger train services from London Euston to Birmingham, Crewe, Liverpool, Manchester and Glasgow.
An Avanti West Coast spokesman said: "We're disappointed TSSA have chosen to ballot their members and remain open to continuing talks with them.
"The pandemic was an unprecedented shock for the railway, with the lowest passenger numbers in over 150 years and record levels of public funding to keep it running.
"Our whole focus now should be securing a thriving future for rail that adapts to new travel patterns and takes no more than its fair share from taxpayers, instead of staging premature industrial action which would disrupt passengers' lives and put the industry's recovery at risk."
