Network Rail is to announce 2,500 job losses in an attempt to cut costs and improve performance.
The job cuts will be phased until 2006 and will be spread across the company according to the Rail, Maritime and Transport Union (RMT).
The company, which employs more than 14,000 workers, is aiming to reduce costs by 20 per cent - £1bn a year - following a huge increase in overhead costs following the demise of Railtrack.
Iain Coucher, Network Rail's deputy chief executive and acting HR director, would not confirm the numbers involved but admitted driving down costs and improving performance are Network Rail's main focus.
"Headcount is something we're looking at as part of our efficiency improvement programme and we hope to release more details of our cost-saving plans early next week", he said.
Bob Crow, general secretary of the RMT, said job cuts on such a big scale would be "obscene".
"It is huge bonuses for the directors and P45s for the rest. We will resist any compulsory redundancies, with industrial action if necessary," he said.