West Bromwich Albion have blocked all ticket orders placed on Viagogo's website for their final game of the season with Manchester United.
Albion have made the move in an attempt to clamp down on United supporters trying to purchase tickets in the home section of The Hawthorns for Sir Alex Ferguson's final game in charge.
The move comes on the same day it was rumoured that Baggies fans have been trying to sell tickets for the match for massive profit.
Despite Viagogo being an official Ticket Exchange Partner, all orders made on the site for the May 19 sell-out visit of the Premier League champions have been blocked.
Any orders lodged on Viagogo after 8am on May 8 - around the time that United confirmed Ferguson's retirement - will not be honoured by Albion.
A club spokesman said: "Viagogo is the official ticket marketplace for the vast majority of Barclays Premier League clubs. The club joined forces with Viagogo at the start of the season to enable season ticket holders to sell their seat to another Albion fan when they cannot make a game. The club verifies all such sales before tickets are distributed.
"We noticed on Wednesday that, within minutes of Manchester United announcing Sir Alex's retirement, there was a huge spike in ticket orders being placed on Viagogo. With Manchester United's help, we have identified that the vast majority of these orders were lodged by United season ticket holders/members.
"Therefore, we will not be honouring any ticket orders lodged after 8am on Wednesday, May 8. This is in keeping with all terms and conditions which stipulate that the club reserves the right not to honour orders from buyers that are suspected to be opposition fans. The safety of fans is paramount, which is why we so vehemently uphold the rules regarding the segregation of supporters."
Albion have also moved to remind all supporters that Stilecards and match tickets should only be sold/assigned/transferred to another Baggies supporter with the prior written consent of the club.
"The club are working closely with the local authorities to limit the potential for away fans to obtain tickets in the home sections," the spokesman added. "We are monitoring all potential platforms - like Ebay - where there is the potential for tickets to fall into the wrong hands. Anyone who sells their ticket for a price greater than face value without the consent of the club is regarded as 'ticket touting', which is a criminal offence."