Chiltern Railways has said it will not be running services between Snow Hill and Moor Street stations and London Marylebone between December 13 and January 8. This affects morning and evening trains which serve Kidderminster, Rowley Regis and Stourbridge Junction.
Birmingham is normally served by at least an hourly service to and from the capital via Leamington Spa and Banbury, with a handful of trains running beyond the second city to Kidderminster via Rowley Regis and Stourbridge Junction.
RMT strike action is due to take place on December 13-14, 16-17 and from 4pm on Christmas Eve until 7am on December 27, as well as January 3-4 and 6-7, while other unions are also set to walk out between next week and January 8.
The rail operator has told customers to "only travel if absolutely essential throughout the whole period of industrial action".
It has also said there will be no services operating north of Banbury from next Tuesday until Sunday, January 8.
In a message on its website, Chiltern Railways added: "Services will operate from around 08:00-16:00 during most of the period of industrial action.
"If your journey is essential and you do decide to travel, plan ahead, allow extra time and expect short notice cancellations and changes."
RMT members continue to strike after rejecting a pay offer from Network Rail earlier this week as the on-going row over pay, jobs and conditions continues, with other operators affected including Avanti West Coast and West Midlands Railway.
Rejecting the latest offer, union chiefs said the Rail Delivery Group's attempts to resolve the dispute with a revised offer were "blocked by the Government".
"The companies know that RMT cannot, and never will, accept the implementation of Driver Only Operation (DOO) as a national principle for operating the railways," the union said.
The smaller TSSA union said it was calling off strike action this month while it balloted its members at Network Rail on the latest offer.