Wanderers sent the letter, addressed from Wanderers CEO John Tsatsimas, ahead of the club's first-ever marquee friendly against Arsenal on Saturday.

Western Sydney are desperate to put a halt to constant anti-social behaviour from a small group of their fans, which according to the five-year club has cost them "immeasurably", both financially and in terms of brand image.

The club has previously been fined heavily and had suspended points deduction imposed, although they are yet to lose any official competition points to date.

Wanderers fans held aloft a homophobic banner during a Sydney Derby in the 2016/17 while flares were let off during an AFC Champions League game and also during two of the club's NSW NPL2 games.

Wanderers fans let off flares during ACL matchday six

The letter called for a "new era in active support", threatening to close down the RBB should any more incidents occur.

"It is quite clear that this cannot continue and such behaviour will not be accepted at our matches," the letter read.

"Notice is hereby given that should any of these incidents happen this season, including use of flares or other incendiary devices, violence, pitch invasion, discriminatory behaviour or acts that constitute a failure to live up to the terms of admission into the venue, then the club reserves the right to close down the active support area for an indefinite period as outlined by the club which will lead to the redeployment of non-offending Members to other available seating in the Stadiums during this closure.

"To assist in the prevention of any such closure we are seeking those who feel passionately about the Western Sydney Wanderers Football Club and wish to lead this active support change to come forward and take part in the evolution of active support at Western Sydney Wanderers matches."

Wanderers will hold a Members Forum at Club Marconi on July 25 where those interested can participate.

Wanderers supporters

The club reiterated the necessity for new leadership among their active supporter base, ahead of the return to the revamped Parramatta Stadium in 2019.

"With a safe standing section lobbied for by the club and included in the design for Western Sydney Stadium we want to see active support and our match day atmosphere taken to the next level," the letter read.

"To make that happen we need a leadership within the group willing to work with, not against the club.

"The reality is that further major incidents that affect the image and reputation of our club may result in the indefinite closure of active support."