After negotiations to end a severe dispute over pay, jobs and conditions failed, thousands of railway workers are striking for the second time this week today (Thursday 23 June).
RMT union members at Network Rail and 13 train operators are involved in the industrial action, which will severely disrupt rail services throughout the UK.
Only about one in five trains will run, mostly during the day on main lines.
But what is the RMT union? What does it stand for, and when was it founded?
Here is everything you need to know.
What does RMT stand for?
The RMT union’s full title is the National Union of Rail, Maritime and Transport Workers.
It is a British trade union covering the transport sector.
When was it formed?
The RMT was formed in 1990 through a merger of the National Union of Railwaymen and the National Union of Seamen to create a single transport industry trade union.
Although a sizable number of its members work on the railroads (the union is the largest of the three railroad trade unions), a growing portion of its membership works in sectors related to the broader field of transportation.
Privatisation and the division of organisations like the National Bus Company and Associated British Ports have grown membership numbers in these sectors.
The RMT now represents more than 80,000 members across nearly all facets of the transportation sector.
How is it structured?
RMT members are spread over 200 branches across the nation, and these are organised geographically into eleven Regional Councils.
The Union's current headquarters are located just off London’s Euston Road, at Unity House.
Who is Mick Lynch?
The union’s current General Secretary is Mick Lynch, a British trade unionist who was born and raised in the Paddington area of London.
Lynch’s first dalliance with the unions came when he was working in construction and joined a union, and was unlawfully blacklisted as a result.
He started working for Eurostar in 1993 after being unable to find employment in the construction industry, and it was here that he first got involved with the RMT.
Lynch went on to serve two terms as Assistant General Secretary of the RMT, and two terms on its executive, and was selected as the union's acting general secretary in 2020 when his predeccessor had to take a leave of absence owing to illness.
However, he stood down after a few months, accusing members of the union's national executive of bullying and harassment, but would win an election for the permanent role of General Secretary in May 2021.
Lynch has received a lot of attention for his appearances in interviews and debates during the media coverage of the RMT's 2022 strikes.
He has found himself facing a bizarre line of questioning and has become a hit on social media with his combative media exchanges.
One of the strangest moments came when Piers Morgan suggested Lynch's Facebook profile picture of Thunderbirds villain The Hood meant he was aligned with a "evil, criminal, terrorist mastermind”...
More on Mick Lynch: Who is Mick Lynch? What did RMT union leader say in Kay Burley rail strike interview?
How do I join the union?
If you work in a relevant transport sector, you can join the RMT on its official website.