The biggest rail workers' union in the UK has rejected the offer of a pay rise from train operators.
The Rail Delivery Group (RDG) offered an 8% pay increase and a guarantee of no compulsory redundancies on Sunday.
But the offer was rejected within hours by the Rail, Maritime and Transport union (RMT), meaning planned strike action is set to go ahead in the run-up to Christmas.
Here is what passengers need to know about the strikes.
When are the rail strikes before Christmas?
Two 48-hour periods of strike action are scheduled to take place on 13-14 December and 16-17 December.
Members of the RMT voted in favour of more strike action at Network Rail and 14 train companies.
Previous RMT strikes have caused huge disruption on train services across England, Scotland and Wales.
Are there any strikes planned for after Christmas?
There are further national strikes planned by the RMT for the new year.
Two more 48-hour walkouts are scheduled on 3-4 January and 6-7 January.
Are there are any other strikes around Christmas?
Yes. There are two regional strikes planned before Christmas.
The first is an RMT strike on 11 and 12 December that will affect the Avanti West Coast train line.
Another strike by the Unite union will take place on East Midlands Railway on 23 and 24 December.
What happened with the latest pay offer?
The RMT strikes have been called because of a long-running dispute over pay, jobs and conditions.
The union rejected the RDG's offer on Sunday evening.
The RMT said: "The RDG is offering 4% in 2022 and 2023 which is conditional on RMT members accepting vast changes to working practices, huge job losses, Driver Only Operated (DOO) trains on all companies and the closure of all ticket offices."
RMT general secretary Mick Lynch said: "We have rejected this offer as it does not meet any of our criteria for securing a settlement on long-term job security, a decent pay rise and protecting working conditions.
"The RDG and Department of Transport, who sets their mandate, both knew this offer would not be acceptable to RMT members."
He said the RMT is demanding an urgent meeting with the RDG on Monday morning "with a view to securing a negotiated settlement on job security, working conditions and pay".
What did the rail operators say?
The RDG said the strikes, coupled with an overtime ban over Christmas, would result in a month of disruption on the network.
A spokesperson said: "This is a fair and affordable offer in challenging times, providing a significant uplift in salary for staff.
"If approved by the RMT, implementation could be fast-tracked to ensure staff go into Christmas secure in the knowledge that they will receive this enhanced pay award early in the new year alongside a guarantee of job security until April 2024."
What has the government said?
Transport secretary Mark Harper said the union's announcement was "incredibly disappointing" and was unfair to the public, passengers and the rail workforce.
"Our railways need to modernise. There's no place for outdated working practices that rely on voluntary overtime to run a reliable seven-day service," he said.
Watch: RMT says rail strike talks are 'definitely moving'