The Venezuelan government has ordered three privately-owned television stations to pay up to $2m in taxes for airing opposition ads free of charge.
Chavez is locked in a fight with private media
The stations broadcast opposition endorsements of a strike in late 2002, which had been called to try to force President Hugo Chavez from office.
The stations are Venevision, Televen and Radio Caracas Television (RCTV).
RCTV called the move a bid to silence the media, which Mr Chavez accuses of supporting efforts to overthrow him.
"This is a strike against freedom of expression," RCTV Director Marcel Granier told Reuters news agency as tax inspectors arrived at the station's studios.
Officials said the free broadcasts were a taxable item under the law.
Most private television, radio and newspaper companies in Venezuela openly oppose the government.
They often echo opposition leaders who denounce Mr Chavez as an authoritarian ruler and a communist sympathiser.
The president has vowed to shut down channels he says foment revolt against his government.
He has yet to carry out those threats.
But last October officials seized equipment from the 24-hour news channel Globovision, known for its criticism of Mr Chavez.