A High Court justice has dismissed a Russian news service's complaint that a £200,000 fine imposed by Ofcom last year was disproportionate.
The court endorsed the media watchdog's decision to fine RT, formerly Russia Today, for "a serious breach" of its impartiality rules.
The regulator said RT's "failures" had been "serious and repeated".
"We welcome today’s judgement that our investigations and decisions were fair and proportionate."
RT has yet to respond to the ruling.
Following an investigation in 2018, Ofcom found that RT had broken TV impartiality rules in seven programmes discussing the Salisbury nerve agent attacks.
Ofcom said RT had failed to give due weight to a wide range of voices on a matter of major political controversy.
The Kremlin-backed station, which aims to provide the Russian viewpoint on global events, is available in more than 100 countries.
In its submission to the High Court, RT had claimed it had not needed to include "the dominant media narrative" that Russia had been behind the Salisbury attacks.
It claimed Ofcom's decisions were "a disproportionate interference with RT's right to freedom of expression" and said other stations had received smaller fines for more serious breaches.
In his 33-page ruling, however, Lord Justice Dingemans said the broadcasting regulator was entitled to impose the "proportionate" financial penalty.