Venezuela's government has increasingly clashed with private media that Chavez accuses of conspiring against him.
The series of investigations into Globovision, the only fiercely anti-Chavez channel remaining on the open airwaves, could lead to its closure.
Regulators have shut down 32 radio stations since July and two small television stations while opening investigations of more than 200 others.
The action against Globovision came the same day government and opposition supporters took to the streets of Caracas, Venezuela's capital, and a day after protests were held in several cities against Chavez.
Leaders of the Democratic Alternative, a coalition of opposition groups, headed a large demonstration against a new education law approved last month.
Opponents say the law contains provisions intended to indoctrinate students.
In recent weeks police have arrested at least 11 people demonstrating against the measure at various protests, further angering Chavez opponents.
Antonio Ledezma, the Caracas mayor, said, addressing Chavez at the rally: "If you want peace, open the paths to dialogue."
Ledezma, a leading opposition figure, urged the president "to end the persecution of mayors and governors" that oppose the government.
In other parts of Caracas, Chavez supporters, led by several cabinet ministers, took to the streets to voice support for the president's policies and denounce "imperialism".