“If this report is accurate, then it describes an unacceptable breakdown in the barrier between foreign intelligence surveillance and criminal process,” the letter stated. “If the government has institutionalized the sharing of foreign intelligence information across agencies to aid in the routine criminal prosecution of U.S. persons, then we will be forced to take a closer look at those assurances.”

The congressmen also said that recent reports state that federal agents have been trained in “fabricating” alternate routes by which the information could have been obtained, rather than disclosing that the data came from the NSA.

“The idea that federal agents devise ‘parallel’ storylines to avoid this disclosure is deeply troubling,” the lawmakers wrote. “It also raises constitutional questions. As a matter of due process, a criminal defendant has a right to know how the government has obtained the evidence used against him, and the government has an obligation to disclose those sources.”

The lawmakers demanded that the DOJ launch an investigation into the issue and publicly report its findings.

“The public deserves a full explanation of the use of these surveillance programs,” the letter stated. 

The lawmakers asked Holder to respond to their request by Aug. 26.

Criticism of NSA surveillance programs has grown as more reports become public that the agency has gathered data about U.S. citizens, not just foreigners suspected of being involved in terrorist plots.