The governing body confirmed the Sharks would be slugged $30,000 and the Sea Eagles $20,000 after Cronulla coach Shane Flanagan and Manly's Trent Barrett both lashed the whistleblowers after their week-one finals exits.
Both clubs appealed their penalties after they were handed down a fortnight ago, however NRL head of football Brian Canavan said neither would be granted reductions in their fines.
"Given the seriousness of the breaches - and the need for the integrity of the game to be maintained - it was decided that the penalties should stand," Canavan said.