Thai authorities searched the premises media outlet Prachathai Tuesday, two days after one of its journalists was arrested, it tweeted.
Soldiers and police were searching for "documents and subversive materials that may incite the public to not accept the draft constitution," according to the warrant, seen by dpa.
The search comes two days after a Prachathai journalist was arrested for possessing pamphlets and other documents that discussed the constitution.
The junta has banned public discussion of both the constitution and the referendum and arrested activists and politicians found violating its order.
Critics argue that such actions prohibit a discussion of the proposed constitution, which they say is undemocratic.
According to activists and both major political parties, the draft constitution will prolong military rule by allowing for a fully appointed upper house of parliament and provisions for an unelected prime minister.