Thousands of commuters on one of the busiest rail routes in the South East will face major disruption next week as part of a £300m improvement project.
There will be no direct trains between London and Brighton and between Lewes or Eastbourne and the city from Sunday.
Network Rail said surrounding services would be affected while engineers renew and upgrade the Brighton Main Line.
It said season-ticket holders would not be compensated because alternative journeys were being provided.
The nine-day closure until 24 February coincides with the school half term when Network Rail hopes passenger numbers will be lower and some people will be able to be more flexible with their travel plans or take annual leave.
The £67m upgrade is the biggest refurbishment of the line – which is used by more than 300,000 passengers per day and renowned for being one of the most unreliable parts of the network – in more than 30 years.
Network Rail said without the programme of work, reliability on the line would deteriorate in the months and years ahead, leading to more delays for passengers travelling between London and the south coast.
Summer Dean, from the Association of British Commuters, said it was unacceptable that season-ticket holders would be left “out of pocket”.
“They have paid a lot of money… and they’re not going to be getting that service,” she said.
“They’re going to have to pay for things like alternative travel accommodation to be able to go about their daily business in the city.”
Network Rail said compensation was not available for the days affected by line closures because passengers “will be provided with alternatives to complete their journeys, including rail replacement bus/coach services or diverted trains”.