The line is closed on Great Western Railway's services between Westbury and Chippenham due to a staff shortage.
Train services running through these stations are cancelled - the disruption is expected until 18:15.
A replacement bus service is running to take passengers between the two towns via Trowbridge and Melksham.
More top news
Largely cloudy but spells of sunshine breaking through.
ITV news has seen letters sent to three unions which reveal more than 12,400 planned redundancies.
Coastguards called the behaviour "unacceptable" as it revealed details of the incident near Brixham on its social media page.