The founders of the opposition-research firm that produced the dossier alleging ties between President Donald Trump’s campaign team and Russia will invoke constitutional privileges and decline to testify before the House Intelligence Committee, their attorney wrote in a letter obtained by Business Insider on Monday.

“We cannot in good conscience do anything but advise our clients to stand on their constitutional privileges, the attorney work product doctrine and contractual obligations,” Fusion GPS’ counsel Josh Levy wrote in response to subpoenas issued earlier this month by the committee’s chairman, Rep. Devin Nunes.

Levy argued that complying with the subpoenas would violate “the First Amendment rights” of the founders — Glenn Simpson, Thomas Catan, and Peter Fritsch — “and would chill any American running for office … from conducting confidential opposition research in an election.”

“Should you compel any of our three clients to appear at the scheduled deposition, they will invoke their constitutional privileges not to testify,” Levy wrote. “Since that will be the case, we ask that the Committee excuse them from appearing.”