Thirty-four female middle managers will be claiming £25,000 each against their employer, Network Rail, after a survey by their union found that women in the organisation earned on average £4,500 a year less than their male counterparts.

The Transport Salaried Staffs’ Association (TSSA) has deemed the gap in salaries “unacceptable” and Network Rail has agreed to work with the TSSA to review its systems, saying that it is “committed to fair pay.”

Outlining the details of the case at its annual conference in Cardiff yesterday, TSSA general secretary, Manual Cortes said that the 34 women are “the tip of the iceberg” and that claims amounting to £25m could eventually be brought against National Rail (NR).

Speaking of the gap n salaries, Mr Cortes said: “That is just an average figure, in some cases the gap is as high as £10,000. This is completely unacceptable in a firm which receives the majority of its funding from the taxpayer.

“We are determined to end women being treated as second class citizens in the rail industry when it comes to pay. NR should set an example to the rest of the industry, bearing in mind the Equal Pay Act became the law of the land more than 35 years ago.”

Since David Higgins joined NR as chief executive in 2011 the company has been undergoing an internal review addressing “diversity and inclusion” and has recently been trying to recruit more female employees.

The claim will be the “largest ever’ equal pay dispute in the rail industry and will be filed later this month at a central London employment tribunal.  If it goes to arbitration it could take a very long time to settle but the union would prefer to open talks rather than pursue a legal settlement.