Ziad El Heni was placed in police custody after being questioned on Tuesday evening about alleged "crimes through telecommunications" channels, his lawyer Dalila Msaddek told AFP.
The interrogation took place after El Heni mocked an article of Tunisia's penal code related to criticizing the head of state, currently President Kais Saied, on his morning radio show on the private station IFM.
The article in question punishes anyone guilty of insulting the head of state with up to three years in prison.
The lawyer said she was only able to speak to her client for "30 seconds" at the police station where he was questioned. She said she refused to sign the document authorizing his detention.
The SNJT journalists' union called for El Heni's release in a statement, describing his arrest as "a flagrant violation of the law."
The union called on its members to gather on Thursday at the court where the journalist is due to appear to demand his release.
In May, journalists staged a protest to denounce the Tunisian government's "repressive" policy, which they say uses the judicial system to intimidate and subjugate the media.
Around 20 journalists are being prosecuted for their work, according to the union.
Non-governmental organizations have reported a decline in press freedom in Tunisia since Saied assumed full powers in July 2021.
Tunisia Journalist Jailed Over Criticism
FILE: Representative image of police handcuffs. Taken Feb. 2, 2023
TUNIS — Tunisian journalist Zied El Heni was arrested after criticizing the penal code which criminalizes insulting the head of state during a radio broadcast, his lawyer said Wednesday.