The Interior Ministry says Ettarik Al-Jadid paper broke election rules by publishing candidates' platforms before the official start of the campaign.
The paper is the mouthpiece for the Ettajdid party, whose candidate, Ahmed Brahim, is challenging President Zine El Abidine Ben Ali.
Hatem Chaabouni of Ettajdid said Monday that the government was pressuring the party by seizing the papers this weekend.
Ben Ali won power in a 1987 palace coup and has won every election since by a landslide, amid suspicions of fraud. Three low-profile candidates have been allowed to run against him.