The EU has said it considers the move to be a form of blackmail.
How has Russia halted gas flows?
Despite the invasion of Ukraine, Russia has continued to supply a large amount of gas to many European countries.
However, after Western powers placed financial sanctions on Russia, President Putin announced that "unfriendly" countries would have to pay for gas in the Russian currency.
The Russian-state-owned energy company Gazprom says it has cut off supplies to Poland and Bulgaria and will not restart these until payments are made in roubles.
Who's paying in roubles?
EU Commission president Ursula von der Leyen warned that complying with Russian demands would breach EU sanctions and would be "high risk" for companies that did so.
Gas companies in some EU countries, including Germany, Hungary and Slovakia, have agreed to pay for gas in euros through Russian bank Gazprombank, which will then convert the payments into roubles.
The Financial Times has reported that gas companies in Austria and Italy are also planning to open accounts with Gazprombank.
The EU said last week that if buyers of Russian gas could complete payments in euros and get confirmation of this before any conversion into roubles took place, that would not breach sanctions.
However there are different views among countries on how to interpret its initial guidance, and EU diplomats have said they want more clarity on the issue.
How much gas does Russia supply to Europe?
In 2019 Russia accounted for 41% of the EU's natural gas imports.
If Russian gas supplies to Europe dried up, Italy and Germany would be especially vulnerable as they import the most gas.
