In a proposed issue of first impression, the attorney for a New York stockbroker nabbed in a U.S. Securities and Exchange Commission enforcement action is asking a Manhattan-based appeals court to render a commonly used tool for extending the agency’s investigations unenforceable in federal court.

The novel argument, which takes aim at the validity of so-called tolling agreements allowing the SEC to extend the statutory five-year window for filing an enforcement action, has never before been offered in court, and very little has been written on the subject.