A council has referred itself to a watchdog over claims that one of its officers read a councillor's confidential email without consent.
Ed Fordham said a message sent to his Derbyshire County Council email from a group was intercepted by an officer.
The Brockwell ward councillor believes data protection laws were breached.
The council said its accounts had at least one delegate who can access them if the main account holder is unavailable.
According to the Local Democracy Reporting Service (LDRS), councillor Fordham, leader of the Liberal Democrats at the council, said he realised his email had been read after an officer responded to it before he had a chance to.
When he questioned it, he said he was "stunned" to be told the authority employed staff, who can access and read all 64 county councillors' emails.
Mr Fordham said: "What Derbyshire County Council has been doing is out of order, ethically wrong and without the very basic principle of consent.
"This is a scandal.
"There have been concerns for some time that emails of councillors have been interfered with, but it has been largely dismissed."
He said the email contained bank details of a local group applying for funding.
The authority said it employed 11 secretaries, personal assistants and member support officers at a combined cost of £213,000 a year to carry out administrative work and other duties on behalf of councillors.
A council spokesperson added: "It is Derbyshire County Council policy that each DCC email account has at least one delegate (someone who can access the account if the main account holder is unavailable).
"This has always been the case for councillors and officers and is a system that has worked well.
"When councillors are elected they are told what PA support they will have, who that will be, what support is provided and how that support is delivered."
However, Mr Fordham is adamant permission to read his emails was never asked for or given, and believes the council is in breach of Data Protection Law and General Data Protection Regulation.
He has now told the council to cease unauthorised access to the emails of Liberal Democrat councillors and tabled a motion to the next meeting of full council on 1 December to stop access to members' emails across all parties.
The council said its data protection officer (DPO) had already carried out a review and made a number of recommendations to ensure greater transparency following the issue raised by Mr Fordham.
"These include ensuring appropriate dialogue between individual members and their allocated support officers to agree the nature and extent of the administrative support provided to enable them to carry out their public duties effectively," the spokesperson said.
They added the DPO was "satisfied that there is a lawful basis for processing information in this way".
The authority has referred itself to the Information Commissioner's Office (ICO) after Mr Fordham called for a "genuinely independent investigation" to take place.