Russia has been under the jurisdiction of the European Court of Human Rights -- overseen by the continent's top rights organisation -- for more than 20 years, becoming its biggest purveyor of cases.
But after the 2014 annexation of Crimea ties between Moscow and the Council of Europe reached a crisis point, and Russia may quit the rights body or be suspended this year, activists and observers warn.
"For Vladimir Putin, Council of Europe membership is certainly seen as being part of the civilised world and an exit has always been considered an unwelcome scenario," said Tatyana Stanovaya, head of R.Politik, a Paris-based analysis firm.
"However there may not be another way out in the current circumstances."
A Russian departure -- dubbed "Ruxit" by the council's secretary general Thorbjorn Jagland -- would have far-reaching consequences.
Campaigners warn of a potential intensification of a clampdown on civil society, worsening abuse of prisoners, a new wave of emigration, and a possible reinstatement of the death penalty.
Ruxit would also weaken the council itself, and create new fault lines in Europe.
After Moscow's annexation of Crimea from Ukraine, the Parliamentary Assembly of the Council of Europe deprived the Russian delegation of voting and other rights.
In retaliation Russia has suspended its annual 33 million euro ($37 million) payment to the Strasbourg-based council -- about seven percent of its budget -- and has not participated in PACE sessions.
As a result more than half of ECHR judges, who serve for non-renewable nine-year terms, and the Commissioner for Human Rights have been elected without Russia.
After two years of non-payment of contributions -- from June this year -- Russia could be suspended from the council.
More importantly, Moscow probably will not be able to participate in the June election of the council's next secretary general, and Russia warns that if this happens it may go.
Pyotr Tolstoy, deputy speaker of parliament's lower house and head of the country's PACE delegation, said Moscow would take part in the election only if all its rights were restored and if PACE agreed to eliminate a possibility to impose sanctions against national delegations.
"If this does not happen, the Russian delegation will not take part in the election," Tolstoy told AFP.
"This brings into question the overall necessity of our participation in this organisation."
Russia's top opposition politician Alexei Navalny, who has filed many complaints with the court on behalf of himself and others, said Moscow may be bluffing.
"The Kremlin is relishing the fact that our delegation has been deprived of voting rights," Navalny told AFP in an interview, noting that the Kremlin uses tensions with Europe to boost its standing at home.
"Even though the Russian government really does not like many of the ECHR decisions, they don't want to withdraw from the Council of Europe, and the Council of Europe does not really want to exclude Russia," he said, suggesting that rules could be bent to keep Moscow in the organisation.
Rights attorney Karinna Moskalenko, the first Russian lawyer to win a case at the ECHR, said that even if Moscow was playing a game it was a "very dangerous" one.
"They may reach a point of no return," said Moskalenko.
The 47-member council -- which is not linked to the European Union -- promotes democracy and the rule of law across Europe and also includes Turkey and Ukraine.
Were Russia to leave the council, it would only be the second such case in its 70-year history. Greece quit the body under the military junta in 1969 to pre-empt being kicked out, but was re-admitted in 1974.
Talks to resolve the crisis are underway but the margin of manoeuvre is very small, said rights activists, noting the organisation may not be in a position to fulfil all Russian demands.
Council of Europe spokesman Daniel Holtgen said the organisation was hoping to find a solution by May when the council's decision-making body meets. He stressed Russia took part in all of the council's bodies except PACE.
Late last year more than 60 campaigners and lawyers signed a memorandum calling on both sides to find a compromise, saying Russia's departure would punish victims of unfair prosecution and trials.
They also warned of a potential reinstatement of the death penalty, which must be banned as a prerequisite for council membership.
"It is quite obvious that the losses will be huge," said Yuri Dzhibladze, president of the Centre for the Development of Democracy and Human Rights, calling the court "an ultimate hope for justice".
In 2017 alone, the Russian government paid more than 14.5 million euros in "just satisfaction" to victims, compared with 222,667 euros for Britain and 88,279 euros for France.
Russia has made a point of paying but it often fails to act to root out the cause of problems behind violations, activists say.
Tolstoy dismissed campaigners' worries, saying Russia's courts and law-enforcement bodies were in line with European standards.
"Human rights campaigners simply cannot imagine how they will live without the ECHR, but they will have to live without the ECHR."
Navalny said many Russians lived with the feeling that "somewhere out there, far away in France there is justice" and Moscow's departure would pose a major problem.
"The realisation that fair trial will no longer be available -- even theoretically -- will be the main and most terrible consequence."