The trust, which provides acute and specialist care at hospitals in Gloucester and Cheltenham, has been failing to see some patients in A&E within the national waiting time target of 4 hours. It has been missing this target for the majority of the financial year 2014-15.
Monitor will examine why the trust is consistently failing the national A&E target and what can be done to reduce waiting times for patients.
Paul Streat, Regional Director at Monitor, said:
Some patients at the trust have been waiting too long in A&E, and this has been going on for some time. For the benefit of local people in Gloucestershire, the situation needs to improve soon.
Over the past year we have worked with the trust and local health care organisations to identify what could be done to improve health care across the area, but we now need to look more closely at what the trust could do for its patients in A&E.
No decision has been made by Monitor on whether action will be needed. Monitor will announce the outcome of its investigation once it is completed.