A solicitor from County Londonderry is being questioned by police about serious crime.
Mr Sandhu is being held at Antrim police station
Detectives have been granted more time to question Manmohan Sandhu, 41, from Limavady, at Antrim police station.
His solicitor, Joe Rice, has written to the Law Society complaining about how, he claims, the police gathered evidence in the case.
Mr Rice alleges the police covertly taped confidential conversations between Mr Sandhu and his clients.
He said those conversations, allegedly taped at Antrim police station, led to Mr Sandhu being questioned about serious terrorist activity including membership of a loyalist paramilitary organisation.
The letter from Mr Rice to the Law Society's chief executive also said: "It is a sad day for our criminal justice process that a solicitor cannot guarantee that his advices to his client in a police station may not be free from state interference."
He also states: "I am sure you will share my concern that the right to confidentiality that must exist between solicitor and client has now been eradicated.
"This is a deliberate move by the authorities and no solicitor can at present guarantee his client that any pre-interview or indeed post-interview consultations at police stations in Northern Ireland are private and confidential."