Rail passengers are being advised to check their journeys due to a shortage of train crews, as people celebrate the final of the Euro 2024 championship.
Struggling with staff sickness, Great Western Railway (GWR) said there was a reduction in staff available to take on overtime shifts due to England competing against Spain in the final.
It said services between London Paddington, Bristol and Swindon were likely to be affected.
The shortage is also due to engineering work in Oxfordshire and the Severn Tunnel, which means more train crew are required to run services.
Services between Swindon, Cheltenham and Gloucester are also likely to be affected and GWR said they would implement contingency plans to minimise disruption for customers.
GWR said the contingency plans were likely to impact the frequency of branch line services, with the possibility of short-notice cancellations and alterations.
On some lines, the cancellations could lead to services being reduced to one train every two hours.
Passengers travelling between Bristol Temple Means, Taunton and Exeter, are also being asked to check before they make their journey.
Tickets issued for Sunday are able to be used on Monday, to help customers, GWR said.