Editors at a Russian cable news channel fear the station faces imminent closure after a "political attack" on one of the few remaining sources of objective reporting in the country.

Three cable providers say they will cut TV Rain, a privately run channel, from its packages, after the channel ran an online poll asking whether the Soviets should have surrendered Leningrad during the second world war in order to save hundreds of thousands of lives.

Two providers have already stopped showing the channel, and a third is planning to pull the plug on Thursday.

The poll appeared on the station's website on Monday – the 70th anniversary of the end of the siege of Leningrad. Around 800,000 people died of starvation in one of the most horrific chapters of the war as the city was besieged by the Nazis for two and a half years. The poll was later removed and editors issued an apology for offence caused.

Vladimir Putin's spokesperson Dmitry Peskov said on Wednesday he did not know whether the channel had broken any laws, but was certain it had crossed a moral red line. "As soon as we become tolerant to this kind of survey, we will see the start of the erosion of the nation, and of our genetic memory," he said.

Irina Yarovaya, an MP from the pro-Kremlin United Russia party, said earlier in the week the poll should be seen as a "crime aimed at rehabilitating Nazism" and was "directly insulting to the sacred memory of the war".

The cable provider NTV Plus, which plans to stop broadcasting TV Rain on Thursday, said in a statement the poll about Leningrad had been so offensive it had to act: "This is not about breaking the law … When we distribute a channel, we have to take into account the opinion of our subscribers. People's opinions are just as important as the law on media."

TV Rain's director-general, Mikhail Zygar, said network operators had privately admitted they had made their decisions after receiving phonecalls from the presidential administration.

"We have heard that some people in the Kremlin are unhappy with some of our investigations, and I'm absolutely certain that the Leningrad poll is just an excuse," he said.

While so far there is no talk of fully closing down the channel, Zygar said it could become impossible to continue if cable operators refused to carry it. Advertising revenues would decline both because of lower viewing figures and because people would be scared to be associated with the channel, he said.

TV Rain was initially an internet-only channel but was picked up by a number of cable providers and is the favourite source of news for the so-called "creative class", who were at the centre of anti-Putin protests that swept Russia two years ago.

Ksenia Sobchak, a socialite turned journalist with opposition sympathies, said during her programme on Wednesday night that it was clear this was a "politicised assault" on the channel, and appealed to viewers to come to the rescue.

"Today was the first big attack on TV Rain since it opened," she said. "I want to appeal to our viewers, because we have no one else to rely on. Call your operators and ask them that they don't remove us. If you don't support us, nobody will."