Red Bull has been accused of using "wide-boy" tactics in a bid to discredit a rival brand after it secured a listing with Wetherspoons.
Last month the managed pub giant replaced Red Bull with Monster Energy in all of its 783 pubs.
And evidence suggests Red Bull embarked on a clandestine campaign in a bid get the drink back in the pubs.
An email briefing leaked to The Publican shows that students employed by Red Bull were instructed to 'smuggle' Red Bull into JD Wetherspoons outlets.
They were then asked to take photographs featuring Red Bull cans and tell customers and staff that they have brought it in because they do not like the taste of Monster Energy.
The briefing goes on to instruct the students to deny they work for Red Bull.
Monster's European on premise director Alan Clark hit out at Red Bull's tactics.
He said: "We are extremely disappointed Red Bull has stooped to such desperate tactics in order to try and win back a lost account.
"The reality is that Monster Energy has already achieved a faster rate of sale than Red Bull had previously in JD Wetherspoon so it appears the Monster brand has been very well received by JDWetherspoon customers and the switch has been a great success."
And a spokesman for Wetherspoons added: "Wetherspoon is surprised that a big company like Red Bull would stoop to wide-boy tactics. It confirms what we thought. Monster is the better product.
"That is why we switched. Since introducing Monster, sales (of Monster) have outstripped Red Bull significantly."
It is understood that Red Bull has since stopped the activity. The Publican has contacted Red Bull but the company has yet to provide a comment.