London Irish insist they will "consider all options" after Gloucester announced the appointment of their forwards coach George Skivington as the new head coach at Kingsholm.
The Cherry and Whites had earlier announced Skivington as the replacement for Johan Ackermann, who ended his three-year tenure in the post last month.
Ackermann has taken a role at Japanese Top League side NTT DoCoMo Red Hurricanes, and Gloucester are in the process of overhauling their leadership set-up, with David Humphreys set to step aside as the club's director of rugby.
But the Exiles were not happy with Gloucester's appointment, suggesting they had breached the Premiership Rugby code of conduct regarding inducement and approaches to a coach.
The Exiles revealed Skivington was under contract until the summer of 2021 and that there was no approach from Gloucester's management requesting permission to speak to the coach.
Chief executive Brian Facer said on the London Irish website: "To say we are disappointed with Gloucester's announcement is an understatement.
"George is well liked and respected, and it is understandable that we would not want to lose him, especially so close to the resumption of play after the lockdown. We also know that he is an ambitious young man who would relish the opportunity of being the head coach of a club someday.
"However, the protocols are clear that a club must be approached in writing when there are more than six months remaining on the relevant contract, regardless of whether it is a player or coach.
"George is under contract with London Irish until June 2021 and has not served us with the required notice period, nor have the terms of his contract been breached. More importantly, at no point have we received any proactive communication whatsoever from Gloucester.
"We therefore believe that Gloucester have breached the Premiership Rugby code of conduct regarding inducement and approaches to a contracted player, member of coaching staff and other contracted person.
"This is a most serious issue so, accordingly, we are reserving our rights to consider all our options under the Premiership Rugby governance protocols and other avenues of redress."
Gloucester have been approached for comment by the PA news agency.
Former Wasps, Leicester and London Irish lock Skivington had earlier spoken of his excitement about taking up his new role at Kingsholm.
The 37-year-old told Gloucester's website: "I've been very impressed with everyone I've met at the club so far, and the vision they have for the club.
"What I particularly liked was how far-reaching the vision is, building from the academy, through the first team, and across the whole club. I can't wait to play my part in it.
"When I was playing, Gloucester was one of a couple of clubs that you never fancied visiting. We want to bring that feeling back to Kingsholm.
"I've had a look at the playing squad, and there are some really great players in there. It doesn't need rebuilding, but there are obviously one or two areas that need some work.
"When Gloucester has been successful it's always been built on having a formidable pack.
"We need to make sure we have a pack that has the kind of reputation that it used to have. When we do that, with the skill and pace of the backs we have at the club, we're going to start getting the results we want again."
