^ This.
NFL Collective Bargaining Agreement
ARTICLE 48
NFLPA AGENT CERTIFICATION
(
link)
Section 2. Enforcement: Under procedures to be established by agreement between the NFL and the NFLPA, the Commissioner shall disapprove any NFL Player Contract(s) between a player and a Club unless such player: (a) is represented in the negotiations with respect to such NFL Player Contract(s) by an agent or representative duly certified by the NFLPA in accordance with the NFLPA agent regulation system and authorized to represent him; or (b) acts on his own behalf in negotiating such NFL Player Contract(s).
Section 3. Penalty: Under procedures to be established by agreement between the NFL and the NFLPA,
the NFL shall impose a fine of $47,000 upon any Club that negotiates any NFL Player Contract(s)
with an agent or representative not certified by the NFLPA in accordance with the NFLPA agent regulation system if, at the time of such negotiations, such Club either (a) knows that such agent or representative has not been so certified or (b) fails to make reasonable inquiry of the NFLPA as to whether such agent or representative has been so certified. Such fine shall not apply, however, if the negotiation in question is the first violation of this Article by the Club during the term of this Agreement. It shall not be a violation of this Article for a Club to negotiate with any person named on (or not deleted from) the most recently published list of agents certified by the NFLPA to represent players. The fine amount set forth in this Section shall increase by 5% each League Year beginning in the 2021 League Year.