Collier-Keywood has been in position since 2023 but will exit on 16 July after deciding not to seek a second term and a replacement will be appointed.
He is the second major figure to leave Welsh rugby’s governing body in recent weeks after Wall also left in March at the end of his tenure.
Former Harlequins chairman Wall has been replaced on an interim basis by Marianne Okland.
Calls for the EGM also followed the WRU’s controversial plan to cut the number of professional teams from four to three by June 2027.
That proposal has been met with criticism, protests and legal action from both Scarlets and Swansea Council.
The potential impact of the latest development on the WRU’s plans to cut a team was not directly addressed in the letter sent by CGRU, but the district urged the WRU to pause its plans for the professional game.
A WRU statement continued: “We want to thank CGRU for the constructive spirit in which they have engaged with us during this process.
“The conversations we have had with clubs and districts across Wales in recent weeks have been the kind of meaningful dialogue Welsh rugby needs, and we are grateful for them.”