The public is getting a peek into the little-known workings of a powerful and mostly invisible government entity. And it is seeing a court whose secret rulings have in effect created a body of law separate from the one on the books — one that gives U.S. spy agencies the authority to collect bulk information about Americans’ medical care, firearms purchases, credit card usage and other interactions with business and commerce, according to Sen. Ron Wyden (D-Ore.).

“The government can get virtually anything,” said Wyden, who as a member of the Senate Intelligence Committee is allowed to read many of the court’s classified rulings. “Health, guns, credit cards — my reading is not what has been done, it’s what can be done.”

Members of Congress from both parties are pursuing legislation to force the court’s orders into the open and have stepped up demands that the Obama administration release at least summaries of the court’s opinions.

Critics, including some with knowledge of the court’s internal operations, say the court has undergone a disturbing shift. It was created in 1978 to handle routine surveillance warrants, but these critics say it is now issuing complex, classified, Supreme Court-style rulings that are quietly expanding the government’s reach into the private lives of unwitting Americans.