Russia will stop sending gas to Poland from Wednesday, the Polish state gas company PGNiG has said.
PGNiG said Russian energy firm Gazprom had told it all gas deliveries to the country would be halted from 08:00 CET (06:00 GMT).
Gazprom has justified the suspension under new rules announced last month, which mean "unfriendly" countries must pay for gas in roubles.
PGNiG has refused to do this.
PGNiG relies on Gazprom for the majority of its gas imports and bought 53% of its imports from the Russian company in the first quarter of this year.
It described the suspension as a breach of contract, adding that the company would take steps to reinstate the flow of gas.
Following the news, Poland's climate ministry said the country's energy supplies were secure.
Climate Minister Anna Moskwa said there was no need to draw gas from reserves and gas to customers would not be cut.
PGNiG said its underground gas storage was almost 80% full and, with summer approaching, demand was lower.
Poland also has alternative supply sources, including a liquefied natural gas (LNG) terminal in Swinoujscie.
And on 1 May, a new gas pipeline connection with Lithuania is due to open that will give Poland access to gas from Lithuania's LNG terminal.
Poland was already planning to stop importing Russian gas by the end of the year, when its long-term supply contract with Gazprom expires.
And a new pipeline delivering gas from Norway, known as the "Baltic Pipe", comes online in October. It should reach full capacity by the end of the year and could replace all Russian deliveries.
Supplies from Russia account for about 40% of the EU's natural gas imports.
However, many countries have pledged to move away from Russian energy in response to its invasion of Ukraine.
The US has declared a complete ban on Russian oil, gas and coal imports.
Meanwhile, the UK is to phase out Russian oil by the end of the year, with gas to follow as soon as possible, and the EU is reducing gas imports by two-thirds.
