Slovakia's left wing Prime Minister Robert Fico on Tuesday threatened to block the sale of a minority share in Slovakia's SPP gas supplier, owned by France's GDF Suez and Germany's E.ON Ruhrgas, if the two firms pushed ahead with a proposed gas price hike.

"Before 10 am (0800 GMT) Wednesday I want written confirmation from the companies that they are dropping the proposals. Otherwise the government will not give its green light ... for the sale of their shares," Fico told reporters in Bratislava.

"If they want to do business with the Czech company, they must send us this declaration," he said.

Since 2002, GDF Suez and E.ON Ruhrgas have controlled 49 percent of SPP, the main supplier of natural gas in Slovakia, and also run it. The remaining 51 percent of SPP's equity is state-controlled.

Both GDF and E.ON are currently in talks with the Czech Energy and Industrial Holding (EPH) on the sale of their SPP share. Bratislava must approve the deal for it to go through.

The SPP board wants to raise household gas prices by up to 25.4 percent in 2013. SPP spokesman Peter Bednar said the "price regulation proposal for next year is legal."

Fico told reporters: "The government sees absolutely no reason why the German and French shareholders are proposing higher gas prices that would be incredibly high for households.

"We cannot respect the arrogant and rogue behaviour of the German and French shareholders," he added.

Fico heads Slovakia's social democratic party Smer-SD and is a harsh critic of privatisation.