The deal to place 10 interceptor missiles in Poland by 2013 was reached in mid-August, and followed the signing of an agreement on July 8 by the U.S. and Czech foreign ministries to place a U.S. radar in the Czech Republic.
"The SLD will insist on parliamentary debates and demand that the government and the president inform us about their talks with the U.S. and how the U.S. missile would help Poland and the Poles," said Tomasz Kalita, the SLD spokesman.
SLD is the largest leftist party in Poland and has 55 seats in the 460-member lower house of the Polish parliament.
"If our proposal does not gain enough support in parliament, we are ready to start gathering citizens' signatures all over the country to conduct a national referendum [on U.S. base issue]," Kalita said.
According to recent public opinion polls, over 66% of residents near the Redzikovo military base in northern Poland, where 10 interceptor missiles will be placed by 2013, are against the deployment of the U.S. base in the region.
Russia has consistently expressed its opposition to the U.S. missile shield, saying it threatens its national security. The U.S. claims the shield is designed to thwart missile attacks by what it calls "rogue states," including Iran.
Russian officials earlier said Moscow could deploy its Iskander tactical missiles and strategic bombers in Belarus and Russia's westernmost exclave of Kaliningrad if Washington succeeded in its missile shield plans in Europe. Moscow also warned it could target its missiles on Poland.