Rail unions have reacted with fury to a government threat to make strike action illegal unless a minimum number of train staff work during a walkout.
Transport Secretary Grant Shapps said a law would protect freight shipments of goods such as food and fuel.
But unions vowed “fierce resistance” to any curb on the right to strike, calling the move “authoritarian” and “desperate nonsense”.
Some 40,000 rail workers are being balloted over taking industrial action.
The ballot of National Union of Rail, Maritime and Transport Workers (RMT) members closes on Tuesday and the results are likely to be known the following day.
The RMT claims that the strike – involving members of 15 train operating companies and Network Rail – could be the biggest “in modern history” and bring the country “to a standstill”.
Mr Shapps told The Sunday Telegraph that unions were using strikes as a first resort rather than a last measure.
He cited a promise that the Conservative Party made in its 2019 manifestothat it “will require that a minimum service operates during transport strikes”.
He told the newspaper: “We had a pledge in there about minimum service levels. If they really got to that point then minimum service levels would be a way to work towards protecting those freight routes and those sorts of things.
“We very much hope they will wake up and smell the coffee.”
However, RMT general secretary Mick Lynch said “any attempt” by Mr Shapps to “make effective strike action illegal on the railways will be met with the fiercest resistance from RMT and the wider trade union movement”.
He was joined by Unite general secretary Sharon Graham who said the union “will confront head-on and by whatever means necessary, any further attacks on the right to strike”.
She called it “a cynical, authoritarian move”, adding: “A worker’s right to withdraw their labour is inalienable in any democracy worth its name.”
Meanwhile, Manuel Cortes, general secretary of the Transport Salaried Staffs’ Association, said: “What we are seeing here is desperate nonsense from the Tories who have chosen to attack working people in our union who kept the railways running every single day of the pandemic.”
In its manifesto, the Conservatives said: “Rail workers deserve a fair deal, but it is not fair to let the trade unions undermine the livelihoods of others.”
The RMT said the strike is over pay, terms and conditions as well as planned job cuts. It said its members are facing “pay freezes, threats to jobs and attacks on their terms and conditions”.
Network Rail plans to shed 2,500 maintenance jobs in order to make £2bn worth of savings.
Network Rail – which maintains the railways and carries out vital functions such as signalling – has not been involved in a national strike since 1994. There are concerns a walkout by its workers could affect both passengers and the movement of goods by train, such as fuel and food.
Although rail makes up a relatively small proportion of all freight, this has been increasing because of the lorry driver shortage, and environmental considerations.