The National Cyber Security Centre and the National Crime Agency are investigating after Gloucester City Council confirmed it was targeted in a 'cyber incident.
The council say the incident which occurred earlier this week is currently causing some disruptions to systems and services.
The authority added it could not provide any further information at this point.
In a statement, the council said: "We are doing all we can to make sure customers can still contact us, but we do ask people to be patient as we put necessary arrangements in place.
"Since Monday, we have been actively working with the National Cyber Security Centre and the National Crime Agency to understand more about the nature of this incident and minimise the impact of it.
"Our main focus for the coming days is to manage urgent customer issues and continue to work with the national agencies to bring our systems back online as quickly as possible, but only once we are confident it is safe to do so.
"Although we can still receive emails and phone calls, it will take longer than normal for us to respond.
"We are taking the situation extremely seriously, and thank you for your co-operation and understanding."