Britain's railways could be brought to a standstill this summer, warns a union, as it begins balloting 40,000 members over nationwide strike action.

The National Union of Rail, Maritime and Transport Workers (RMT) says its proposed action could potentially trigger 'the biggest rail strike in modern history' as it targets both Network Rail and 15 train operating companies over a number of issues relating to job security, pay and conditions.

The union claims Network Rail intends to cut 2,500 maintenance jobs as part of a £2bn reduction in spending on the network while staff working at many train firms, it says, are facing changes to their terms and conditions or what amounts to pay freezes at a time when the cost of living is sky rocketing and inflation is at record levels.

The ballot proposing strike action opened on Tuesday this week and closes on May 24, while today will also see the first online rally for the Defend Rail Jobs Pay and Conditions campaign, that begins at 6pm tonight.

If members vote yes in big enough numbers then a national railway strike could begin as early as June, warn union officials.

An 11-day strike by train cleaners has already begun in a separate dispute over pay with staff employed by contractor Churchill walking out as part of their ongoing fight for a £15-per-hour rate of pay.

Just last week the government launched the Great British Rail Sale as part of a concerted campaign across the UK to encourage more people to use train travel in the wake of the pandemic while train companies have also been doing their own work to encourage commuters back to services after passenger numbers were reportedly at their lowest for 150 years because of lockdown and coronavirus restrictions.

But RMT general secretary Mick Lynch warns a national strike could bring the country to a halt this summer.

He said: "Railway workers have had to contend with pay freezes, the prospect of losing their jobs and repeated attacks on their terms and conditions.

"Train Operating Companies have praised our members for being key workers during the pandemic but have refused to keep staff pay in line with inflation and soaring living costs. As a result, thousands of railway workers have seen their living standards plummet and have run out of patience.

"The way for trade unions to effectively take on the cost-of-living crisis is to stand up for their members at work and take industrial action when employers are not moved by the force of reasoned argument. A national rail strike will bring the country to a standstill, but our members livelihoods and passenger safety are our priorities."

Alongside Network Rail, the 15 train operating companies with staff set to receive ballot papers, because the union is in dispute with them, are Chiltern Railways, Cross Country Trains, Greater Anglia, LNER, East Midlands Railway, c2c, Great Western Railway, Northern Trains, Southeastern Railway, South Western Railway, Island Line, GTR (including Gatwick Express), Transpennine Express, Avanti West Coast and West Midlands Trains.

Network Rail, which has said it won't make any decisions that could make the railways less safe, says it is disappointed with the unions plans to press ahead with the votes for strike action.

Post Office workers are also expected to stage their own one-day strike in a dispute over pay on May 3.

Members of the Communication Workers Union voted overwhelmingly for industrial action, which will now take place at the start of next month.