Unions have condemned plans by National Express to charge for seat reservations on its rail services.

National Express has imposed the highest ever seat booking charge by a private rail company for rail tickets with seat reservations – £5 for a return ticket and £2.50 one-way.

The fee applies to most standard class tickets and will affect thousands of passengers travelling on the East Coast line, which links London with Edinburgh via York and Leeds. Those travelling first class, with season tickets, or who are National Express employees, are exempt from the fee, which is due to be introduced Sunday 17 May.

The Transport & Salaried Staff Association (TSSA) is the union for people working in transport and travel and has condemned the fees. Gerry Doherty, TSSA’s General Secretary, said: “This is an outrageous imposition on millions of passengers and amounts to the fourth increase in overall prices in just five months.

“It is simply mugging passengers for an extra fiver. And it will hit the elderly and families the hardest. They cannot risk being forced to stand on long journeys from Newcastle to London and therefore they will be forced to pay the extra.”

National Express has defended its decision to introduce the charge, which is optional: “We want to improve the on-board environment for our customers. We do find that people are often reserving multiple seats as they’re not sure which train they are going to catch.

“While we understand this, by asking people to pay for a seat reservation seats will no longer be left empty with a reserved sign, therefore being made available for other customers to use,” commented a company spokesperson.

The TSSA has already campaigned against the number of increases in train fares throughout one single year, however has so far been unsuccessful – already this year, train fares have increased 6% in January and 11% in May, along with a 25% rise in the cost of railcards from Sunday 17 May.

National Express is a transport company that provides bus, coach, airport transfer and train travel to passengers in the UK, US and Spain, employing more than 43,000 people worldwide.