More than 40,000 railway workers are due to walk out on Dec. 13-14, 16-17, 24-27, Jan. 3-4 and 6-7 in a long-running dispute over pay.
On Sunday, the RMT said it had rejected a pay rise offer of 4% in 2022 and 2023 from train operators aimed at heading off the strike action.
The RMT said on Wednesday it had heard from the Rail Delivery Group, which represents train operators, that there would be no revised offer and it had been instead been instructed by the government to "take on the strike action".
"The planned industrial action for RMT train operating company members goes ahead as scheduled as there is no resolution to the dispute," the RMT said in a statement.
"In fact a resolution to the dispute is now further away due to the government’s late intervention in the negotiating process."
The Department for Transport did not have an immediate comment.

epa10349540 Commuters at a train station in London, Britain, 05 December 2022. The RMT (Rail, Maritime and Transport ) union has rejected an offer from train operators aimed at preventing strikes over Christmas, the RMT announced 05 December. EPA-EFE/ANDY RAIN