Michelle Hackman & Dustin Volz:

A law-enforcement arm of the Department of Homeland Security participated in a secret bulk surveillance program that collected millions of records about certain money transfers of some Americans without a warrant, according to officials and a U.S. senator.

The surveillance program, overseen by investigators with U.S. Immigration and Customs Enforcement, collected records of any money transfer greater than $500 to or from Mexico, Sen. Ron Wyden (D., Ore.) said in a letter sent to the DHS inspector general. It also collected information on domestic or international transfers exceeding $500 to or from the states of Arizona, California, New Mexico and Texas.

Officials at the Homeland Security Investigations unit at DHS provided staffers for Mr. Wyden with details about the surveillance activity last month after the senator’s office first contacted the agency seeking information about the previously undisclosed program. The briefing was the first time Congress was made aware of the program’s existence, according to Mr. Wyden’s letter.

“Given the many serious issues raised by this troubling program, I request that you investigate the program’s origins, how the program operated, and whether the program was consistent with agency policy, statutory law, and the Constitution,” Mr. Wyden wrote in his letter to DHS Inspector General Joseph Cuffari, which was reviewed by The Wall Street Journal. Mr. Wyden also asked the inspector general to probe whether Homeland Security Investigations was operating similar programs and to ensure that such activities were subject to congressional oversight.