Warsaw banking sources said last week the government would come under pressure to provide relief for those borrowers after the Swiss franc jumped to 4.2 zlotys from 3.6 on Wednesday following the Swiss National Bank decision to scrap its cap on the currency.

Poland's stock of Swiss franc-denominated mortgages stood at about $36 billion at the end of last November - almost 8 percent of gross domestic product in central Europe's biggest economy.

Poland faces a general election in October.

"If the franc falls below 4 zlotys, the pressure for changes in regulations will be different," Piechocinski, a leader of the Polish Peasants' Party (PSL) party in the government coalition, told a news briefing.

"If it stays (at the current level) longer, then there will be a need to think about a rational support plan, not only because of the creditors, but also because of the banks' condition," he said without elaborating.

The banks with large portfolios of Swiss franc-denominated mortgages are Getin Noble Bank, PKO BP, General Electric's Polish unit BPH, Santander's BZ WBK, Commerzbank's mBank, and BCP's Millennium.

Finance Minister Mateusz Szczurek has called a meeting for Tuesday with the heads of Poland's central bank and commercial banks following the surge in the Swiss franc, saying the meeting would discuss the foreign exchange market.

(Reporting by Marcin Goclowski and by Jakub Iglewski; Editing by Tom Heneghan)