The Brisbane Broncos have blasted the NRL's decision to dock them two competition points for an interchange mix-up and announced they would appeal.

The Broncos have three days to lodge an appeal after the NRL announced the club's punishment for briefly having an extra man on the field in their round three win over Wests Tigers.

Broncos chief executive Bruno Cullen said the matter was in the hands of legal advisers who would seek leave for an appeal in the coming days.

"I'm very, very disappointed and a bit frustrated and non-plussed about it all," he told AAP.

"We intend to fight for the retention of our two points, which we have no doubt we fairly and justly earned. And we believe we have grounds for appeal."

According to NRL guidelines, grounds for an appeal include: an error in law; the determination was unreasonable or insupportable on the evidence; the penalty imposed was manifestly excessive.

"I think we have something to say about the last two of those," Cullen said.

"Quite frankly there's not a bone in my body that makes me understand any part of this decision."

The Broncos had made a detailed submission to the NRL last Thursday in defence of the second-half interchange at Campbelltown Stadium.

Broncos reserve forward Corey Parker took the field while dazed prop Shane Webcke was being assisted off and then went on to score a try in the following passage of play that locked up the scores and proved the match's turning point.

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