Drivers at two rail operators will take industrial action in disputes separate to the ongoing national row over pay.
Aslef said members at Avanti West Coast will strike on 2 July over an attempt to "force through" sick pay changes "without agreement".
It said London North Eastern Railway drivers would also not work overtime from 1 July after the firm failed to stick to "agreed procedures".
Avanti has urged Aslef to "work with us to avoid another summer of disruption".
The firm's managing director Andy Mellors said it was "extremely disappointed" the union had "again chosen to disrupt the travel plans of so many".
"Thousands of customers, who have already bought tickets, will now be forced to make alternative arrangements at a time when we should be working together to encourage more people to travel by train," he added.
Aslef said Avanti West Coast, which runs services between London and Scotland via Birmingham and Manchester, was trying to "force through" sick pay changes"without agreement", while London North Eastern Railway, which runs between the same two destinations via York and Newcastle, had failed to adhere to "agreed procedures".
General secretary Mick Whelan said it was "deeply regrettable" that union members had been "forced to take this action, but our members will not stand by and allow our agreed terms and conditions to be violated".
"We have been coming to the table to try to resolve these disputes for many months, but unless the operators honour the agreements in place with our members, we will be forced to continue taking action," he said.
"The companies know how to avoid this action – it's by honouring their agreements and negotiating fairly with our members."
On Thursday, Aslef members voted to lift a ban on overtime by train drivers at TransPennine Express, which has hit rail services across the north of England.
The national action has seen thousands of services affected in recent months, with the latest wave of strikes coming on 3 June.
Train drivers strike ahead of Eurovision final
Avanti West Coast contract extended by six months
Aslef
Avanti West Coast
London North Eastern Railway
Search for Titanic sub enters decisive phase
The health risks facing the crew of the Titanic sub
Could Russia really play nuclear roulette in Ukraine?
The health risks facing the crew of the Titanic sub
The woman who wants to end abortion in America
Satellite images reveal Ukraine canals drying up
Windrush 75: 'We have put the Great in Britain'
Final Fantasy 16: Trying to regain fans' trust
Fears grow over Indian state on brink of civil war
The draft star and his overdose – a death that changed America
The Gen Xers making mid-life career pivots
The fisherman who found a dead baby in his net
Where tipping can be considered rude
The fading glamour of digital nomadism
Why are there mountains inside Earth?
© 2023 BBC. The BBC is not responsible for the content of external sites. Read about our approach to external linking.
Avanti West Coast: Train drivers to strike over sick pay, Aslef says
