Poland has suspended deliveries of gas to Eastern neighbour Ukraine following a “warning signal” reduction of gas deliveries into Europe from Russia, cutting supplies by up to 45 percent over the past couple of days.

The squeeze on gas, on which Europe depends for electricity and heating, has come against the backdrop of German Chancellor Angela Merkel calling for tough new sanctions against Russia for its perceived role in the Ukraine crisis, reports The Times. Poland reported reductions by 20 percent on Monday, and then another 24 percent on Tuesday. Slovakia had its deliveries reduced by 10 percent, and Germany has also seen an unspecified reduction.

Concerns over European reserves of gas, which will be absolutely crucial in the coming winter months means Poland have been forced to keep the little gas they are now receiving from Russia instead of sending surplus to Ukraine.

Russian energy giant Gazprom stopped the supply of gas to Ukraine after they stopped paying their bills in April this year, at which point they owed Russia $4.5 billion for gas received. This prompted EU nations Germany, Poland and Slovakia to enhance ‘return flows’ in the gas network. This change in piping infrastructure allowed the redirection of their own deliveries of Russian gas back to the Ukraine, who before the war got over half its gas from the Russians.

Gazprom warned back in June that attempting to circumvent Russia’s gas embargo to Ukraine would result in supplies to European countries also being cut and three months later, that threat seems to have been realised. After three days of gas cuts, Gazprom still denies there has been any reduction in deliveries.

While Europe, led by an increasingly forthright German Chancellor, pushes for ever harder sanctions against Russia, Poland appears to be learning what it means to ‘bite the hand that feeds’. Almost a quarter of all Europe’s energy comes from natural gas, and Russia is a crucial supplier to the European market which during the winter season is susceptible to shock.

A June report by the Council of the European Union on Energy Security revealed that if Russia withheld gas during “peak demand in January… almost the entire EU” except for Spain and Portugal would suffer severe energy shortages. In south-eastern nations like Romania and Bulgaria, only 20-40 percent of normal energy levels could be sustained, meaning prolonged power and heating cuts in countries where winter temperatures can reach minus 30 degrees centigrade.

The report also admits that due to the EU Large Combustion Plants Directive, despite being “highly competitive”, significant coal-fired capacities had to be taken offline in the last two years, rendering Europe’s most plentiful and cheapest energy source unable to make up the gas shortfall.