Network Rail workers threw down the first big industrial relations challenge to the Government when they voted overwhelmingly in favour of going on strike over pay.
Members of the Rail, Maritime and Transport (RMT) union backed walkouts by 4-1 on a turnout of 60%, beating planned Government thresholds on strike ballots.
Workers voted by a bigger margin - 92% - for other forms of industrial action, raising the threat of chaos on the railways.
The result was announced within hours of new Business Secretary Sajid Javid saying that the Government will press ahead with introducing new laws to stop public sector strikes going ahead unless they have the support of 40% of workers eligible to vote.
Turnout will have to reach at least 50% of those entitled to vote for a strike to go ahead.
He told the BBC Radio 4 Today programme: “We have already made clear in terms of strike laws that there will be some significant changes.
“We’ve said that there will be a minimum threshold in terms of turnout of 50% of those entitled to vote.
“We have also said that when it comes to essential public services, at least 40% of people need to vote for strike action.
“And we’ve said we’re going to lift the ban on the use of agency staff when strike action takes place.
“That’s something we’ll give more detail on in the Queen’s Speech but it will be a priority. I think it’s also something that needs to be done.”
TUC general secretary Frances O’Grady said: “This is a Government not so much on the side of hard-working people but Britain’s worst bosses - those who want their staff to be on zero-hours contracts, poverty pay and unable to effectively organise in a union so that they can do something about it.
“The Government’s proposals on union ballots will make legal strikes close to impossible. Union negotiators will be left with no more power than Oliver Twist when he asked for more.”
Unison general secretary Dave Prentis said: “The Government has only been in power a matter of days and it has already come down on the side of exploitative bosses.
“These unfair proposals will make it virtually impossible for working people to stand up to their employers when anything goes wrong at work.
“Bad employers will be rubbing their hands together in glee, safe in the knowledge that they can now pretty much treat their staff as they choose - without having to worry about the threat of industrial action.”
The RMT result will now be considered by the union’s executive.
General secretary Mick Cash said: “Our members have decisively rejected the pay package offered by Network Rail. This is a massive mandate for action and shows the anger of safety-critical staff across the rail network at attacks on their standards of living and their job security.
“It is now down to NR to start taking this issue seriously, to understand the deep-seated grievance felt by their staff and to come forward with a renewed offer which protects pay and jobs.”
The Transport Salaried Staffs Association (TSSA) is also balloting its members, with the result due over the next week.
The unions are protesting at a pay offer of £500 this year followed by rises matching RPI inflation over the next three years.
A no-compulsory-redundancy commitment will be extended to the end of 2016 as part of the proposed deal.
A strike by RMT and TSSA members at Network Rail (NR), including signallers, maintenance workers and admin staff, would cripple train services and would also give the new Conservative Government its first battle on the industrial relations front.
The unions would have to give seven days’ notice of any industrial action.
Mr Cash said: “As far as we are concerned, the one-off, non-consolidated, lump-sum payment this year is wholly inadequate and fails to recognise the massive pressures staff are working under to keep services running at a time when the company is generating profits of £1 billion.
“It is our members battling to keep Britain moving around the clock and they deserve a fair share from Network Rail for their incredible efforts.
“In addition, we are extremely concerned that the no-compulsory-redundancy commitment only applies to the first two years of the four-year deal.
“RMT is in no doubt that this leaves operations and maintenance members extremely vulnerable, especially with the continued development of rail operating centres and the ongoing cuts programme at Network Rail.
“Our rail staff deserve a fair reward for the high-pressure, safety-critical work that they undertake day and night and the last thing that we need is a demoralised, burnt-out workforce living in fear for their futures, and the message has come back loud and clear that that is exactly how they feel about the current offer from Network Rail.
“RMT remains available for talks and we hope that the company will appreciate the anger amongst staff at the current offer on pay and conditions from Network Rail reflected in this ballot result and that they will agree to our call to come back to the table with an improved package.”
The RMT has around 16,000 members at NR, working across the company’s operations and maintenance.
Talks were held at the conciliation service Acas but they failed to break the deadlock.