Network Rail managers and technicians are to be balloted for strike action which could disrupt major rail stations and routes.
The vote comes after claims that female staff are being paid as much as £4,000 a year less than male colleagues in the same grade.
A yes vote could lead to disruption at major rail stations in London, Birmingham, Liverpool, Manchester, Glasgow, Edinburgh and Leeds, according to the Transport Salaried Staffs Association.
The union accused NR of refusing to carry out a "fair pay audit" and of imposing a 2.5 per cent wage rise on white collar staff - less than half of a 5.2 per cent rise given to other employees.
"It is almost unbelievable that we are in this dispute more than 30 years after the passing of the Equal Pay Act," said General secretary Gerry Doherty.
"It is even more bizarre that a publicly funded company is arguing that it can treat its female staff as second class citizens on pay because Whitehall has deemed that it is a private company for accountancy purposes.
"We the taxpayer pick up all the bills for NR, including the directors' lavish bonuses, and it has a moral duty to treat all its staff fairly and humanely."
A Network Rail spokesman, said: "A pay award has been made for this year and we have offered discussions to the TSSA about improving how we work together before we can address their claims.
"This ballot is counterproductive in our efforts to forge a better, more productive and modern employer/trade union relationship."
The strike ballot will finish on August 18, and the union will have to give a week's notice of any industrial action.