Senators Richard Blumenthal and Chris Murphy and Representative Joe Courtney on February 15 condemned what they described as Russia's increasing aggression.
U.S. defense officials said the Russian ship had been operating in international waters off the U.S. East Coast.
The ship reportedly made a port call in Cuba previously and after that was detected off Delaware's coast. Courtney said the vessel later was spotted about 50 kilometers from the submarine base in Groton, Connecticut.
The U.S. Navy conducts similar intelligence-gathering operations against Russian military targets, such as its submarine bases, from international waters.
The Democratic congressmen are calling on Republican President Donald Trump to address Russia's actions.
Based on reporting by AP, dpa, and Fox News