Belarus' Interior Ministry has declared followers of the Polish-based television channel Belsat TV "extremist".
Citizens who subscribe to Belsat's social media channels are liable for prosecution, the ministry said.
Belarus already declared Belsat's website and social networks "extremist" last July, but it has now extended the declaration to the channel's online followers.
"Groups of citizens united through the Internet resources 'BELSAT' are recognised as an extremist formation and their activities are prohibited on the territory of the Republic of Belarus," the ministry said on its Telegram channel.
Minsk has already banned dozens of opposition and human rights NGOs and declared nine Telegram channels "extremist", including NEXTA, NEXTA-Live, and LUXTA.
Those found guilty under the ministry decree face up to seven years in prison, but media groups have said the move is a threat to intimidate citizens and stop them from reading independent news.
Belsat -- which has 940,000 followers on Telegram -- has become one of the main platforms for Belarus' opposition since the disputed re-election of President Alexander Lukashenko.
In February, two Polish Belsat journalists were jailed for two years for "violating public order" when they filmed an opposition protest.
The European Union has condemned the jailings as "unacceptable harassment" and called on the Belarusian authorities to "cease their violations of human rights, fundamental freedoms".
President Lukashenko's authoritarian government has waged a violent crackdown on opponents and independent media since last August's vote, which the West says was rigged.
Tens of thousands of people have been detained and rights groups say more than 800 people are now imprisoned as political prisoners.
On Wednesday, a Belarusian court also sentenced two members of a leading human rights organisation to prison terms for supporting opposition demonstrations.