A leading Democratic senator accused the Justice Department on Wednesday of misleading the public on surveillance law, his latest salvo in a long-running campaign to force disclosure of what he terms “secret law” on how authorities collect information on Americans.

In a strongly worded letter to Attorney General Eric H. Holder Jr., Sen. Ron Wyden (Ore.) also for the first time directly links his “secret law” concerns to Section 215 of the USA Patriot Act, a law passed after the 2001 terrorist attacks that greatly expanded U.S. authorities’ ability to collect intelligence in terrorism and foreign intelligence cases.

Section 215 allows the FBI to obtain business records or other “tangible things” as long as a court finds they are relevant to “an authorized investigation . . . to protect against international terrorism or clandestine intelligence activities.” Section 215 orders may be used to obtain car and travel records, for instance, but the full scope of what can be obtained and how the data may be used has never been made clear.

Such details are classified but briefed to members of Congress and a special surveillance court, Department spokesman Dean Boyd said.

Wyden’s concern apparently relates to a classified intelligence-gathering program under Section 215. “Some orders have also been used to support important and highly sensitive intelligence collection operations, on which Congress has been briefed,” Boyd said.

In the letter, Wyden said he was “troubled” to learn that a department spokesman, Boyd, had stated that Section 215 “is not secret law, nor has it been implemented under secret legal opinions by the Justice Department.”

“This statement is . . . extremely misleading,” Wyden said.

He said that in July, then-National Security Agency general counsel Matthew Olsen testified that “significant” Patriot Act interpretations were contained in classified opinions of the Foreign Intelligence Surveillance Court, which vets government applications for surveillance on U.S. soil in foreign intelligence investigations.

“In our judgment, when the government relies on significant interpretations of public statutes that are kept secret from the American public, the government is effectively relying on secret law,” Wyden stated in the letter co-signed by Sen. Mark Udall (D-Colo.).

Boyd said that the statute “does not violate the Constitution, nor has it been used illegally to target Americans.”

Wyden also criticized as misleading the statements from officials that the government’s authority under Section 215 is analogous to the use of a grand jury subpoena. He did not elaborate. He has on other occasions questioned the government’s ability to gather such data to track Americans.