Train driver members of the RMT at 14 rail operators will strike on February 1 and 3 in the long-running dispute over jobs, pay and conditions, the union announced.
General Secretary Mick Lynch said: "Our negotiations will continue with the rail operators to create a package on jobs, conditions and pay that can be offered to our members."
Earlier members of the Aslef union also announced they will walk out on February 1 and 3 - causing widespread travel disruption across the country.
The decision to strike by the RMT coincides with the Trades Union Congress (TUC) national day of action, with several unions co-ordinating strike action.
The protest action by the TUC is in response to anti-strike legislation unveiled by Rishi Sunak's Government to impose minimum service levels on key sectors during day of strike.
On February 1, over 100,000 civil servants will also walkout at 124 Government departments while thousands of teachers at England and Wales will strike.
Rail bosses made an improved pay offer to train drivers earlier this month, with a backdated 4% pay hike over two years and a commitment to no compulsory redundancies until March 2024.
But the offer came with conditions of changes to working conditions which Aslef branded "clearly unacceptable".
Aslef General Secretary Mick Whelan said: "The offer is not acceptable but we are willing to engage in further discussions with the train operating companies."
Mr Whelan added: "Not only is the offer a real-terms pay cut, with inflation running north of 10%, but it came with so many conditions attached that it was clearly unacceptable.
"They want to rip up our terms and conditions in return for a real-terms pay cut.
"It was clearly a rushed offer, made just before our meeting with the minister, and not one, it seems to me, that was designed to be accepted."
He said the only way to end the dispute was for companies to get round the table and get serious on pay.
Earlier a Rail Delivery Group spokesman said: "It's disappointing our fair and affordable offer, which would take average driver base salaries from £60,000 to nearly £65,000 by the end of 2023 pay awards, wasn't put to the Aslef members.
"With taxpayers still funding up to an extra £175 million a month to make up the shortfall in revenue post-Covid, it provided a significant salary uplift while bringing in long overdue, common-sense reforms that would mean more reliable services for passengers.
"Rather than announcing further unnecessary strikes, we ask Aslef to recognise the very real financial challenge the industry is facing and work with us to deliver a better railway with a strong long-term future."
Full list of operators:
Chiltern Railways
Cross Country Trains
Greater Anglia
LNER
East Midlands Railway
c2c
Great Western
Railway
Northern Trains
South Eastern
South Western Railway
Transpennine Express
Avanti West Coast
West Midlands Trains
GTR (including Gatwick Express)
