"It is a black day for the judiciary and freedom of the press. It is a message to journalists: Be silent or your place is in prison," said Jamal Eddine Boughalleb, who is the brother of Mohamed.
Boughalab was detained last month, which the journalists union said was aimed at silencing the voices of journalists.
The imprisonment of Boughalleb reinforces activists' fears that authorities are increasingly restricting freedoms ahead of presidential elections expected this year.
Saied seized extra powers in 2021 when he shut down the elected parliament and moved to rule by decree before assuming authority over the judiciary.
Since Tunisia's 2011 revolution, press freedom has been a key gain for Tunisians and its media has become one of the most open of any Arab state.
However, politicians, journalists and unions say that freedom of the press now faces a serious threat under the rule of Saied. The president, who came to power in 2019 in free elections, who has rejected such accusations, saying he will not become a dictator.
Two more journalists - Shatha Al-Hajj Mubarak and Lotfi Al-Hidouri - are in prison, while other journalists and activists face judicial investigations due to posts on social media or criticism of the authorities in the media.
(Reporting by Tarek Amara)
