Prominent Russian singers Iosif Kobzon and Alla Perfilova, better known by her stage name Valeria, are time-tested friends of the Kremlin.
In March, both signed an open letter backing Russia's annexation of Crimea.
Valeria has publicly praised the Russian government for a number of other controversial moves, including new legislation targeting homosexuals and the jailing of two members of the opposition punk group Pussy Riot.
On October 21, Kobzon and Valeria will perform at London's most prestigious concert venue, the Royal Albert Hall, to the dismay of critics of Russian President Vladimir Putin.
"People who promote what we regard as the Russian government's criminal actions are unwelcome in Western countries," Andrei Sidelnikov, an anti-Putin activist based in London, told RFE/RL. "We believe that people should bear responsibility for their actions and deeds."
Sidelnikov's campaign group, Speak Up!, has spearheaded efforts to have Britain bar both singers from entering the country.
Earlier this month, it delivered a petition to Prime Minister David Cameron calling on Britain to declare Kobzon and Valeria persona non grata.
The petition, which has gathered more than 4,000 signatures online, accuses the singers of "using their popularity and status" to become "propaganda tools for the international treaty-breaking Russian government."
It also accuses them of being "members of the Kremlin's cheerleading team" and urges Britain to follow in the footsteps of Latvia, which has barred both Valria and Kobzon from entering its territory due to their anti-Ukrainian stance.
Sidelnikov says the heavily advertised performance in London amounts to a Kremlin PR coup and undermines Western sanctions against Moscow.
Valeria's producer, her husband, Iosif Prigozhin, has described the event as "support for Russia's image."
Sidelnikov says it also underscores the double-standards practiced by members of the Russian elite who, like Kobzon and Valeria, routinely rail against Western values.
"Such hypocrisy is unacceptable," he added. "In Russia, they declare that Western values are bad, wrong, and not suitable for Russia. Then they travel to Western countries to earn money, spend holidays, and buy real estate."
Singer Oleh Skrypka pulled out of the concert, saying, "It is out of the question. There are people dying in Ukraine now."
Valeria's teenage son Arseniy Shulgin, who is scheduled to play the piano at his mother's concert, studies in Switzerland.
Sidelnikov says Kobzon's daughter, son-in-law, and grandchildren live in London.
The concert, titled "Valeria and Friends," is backed by Russian authorities and is advertised on the website of Rossotrudnichestvo, Russia's federal cultural agency.
A number of Russian pop stars such as Valery Meladze and Stas Piekha are scheduled to perform alongside Kobzon and Valeria.
They will be accompanied by Britain's prestigious Royal Philharmonic Orchestra.
Oleh Skrypka, the front man of the popular Ukrainian rock band Vopli Vidoplyasova, has pulled out of the concert, although Rossotrudnichestvo still lists him as a participant.
"When I agreed to perform, there were not such tense relations between Russia and Ukraine," he said. "I will not take part in a pro-Russian show. It is out of the question. There are people dying in Ukraine now."
Speak Up! activists plan to demonstrate outside the Royal Albert Hall Hall on the evening of the performance.
RFE/RL correspondent Claire Bigg contributed to this report