The NFL has fined the New York Giants $150,000 (£128,000) and their coach Ben McAdoo $50,000 (£40,400) for breaking the rules by using a walkie-talkie.
The incidents occurred during their Week 14 win over the Dallas Cowboys.
The Giants also had their fourth-round pick in the 2017 NFL Draft moved to the end of the round following any compensatory picks, up to 12 selection spots from where the Giants would have drafted.
The hand-held communication device was used for five plays on an early fourth-quarter drive, while the Giants worked to fix McAdoo's malfunctioning standard communications equipment.
The standard system cuts off communications between the coach and quarterback on the field when the play clock reaches 15 seconds. Using a walkie-talkie is prohibited because its use is not controlled by league officials.
"League policy prohibits a coach from using such devices in a game," an NFL spokesman told NFL.com, "because he would not be cut off from talking by the switch operator for the coach-to-player helmet communication system."
The Giants admitted the offence.
"It was a clear violation of the rules, and we accept full responsibility and the penalty," they said.
McAdoo, in his first season as head coach of the Giants (10-4), is one win away from clinching the team's first play-off berth since 2011. A loss by Detroit, Atlanta, Green Bay or Tampa Bay would also clinch a play-off spot for the Giants.