The WRU learnt that these tickets were obtained from a Welsh rugby club, which has been collaborating with VU Limited in order to sell tickets to VU Limited hospitality customers, who have paid for a match-day hospitality package which includes return train travel from London to Cardiff.
Any such individuals should contact the WRU via unofficialticketing@wru.wales if they are concerned about the validity of their tickets.
The governing body of Wales' national sport reserves the right to protect its commercial interests and to enforce its ticket terms and conditions through all options available to it in order to enable all proceeds from the professional game to be retained and invested back into Welsh rugby.
It has also previously obtained High Court injunctions against two other companies in 2017, Trihorn Enterprizes and Evental Ltd (in the latter case, approximately 200 tickets for Wales' Six Nations meeting with Ireland were cancelled for the same reasons), and strongly advises all fans to ensure they only buy tickets from official sources.
In terms of tickets that come as part of a package with hospitality and/or travel included with a match ticket, this means fans should only buy from official Offsite Hospitality Operator, Events International, Gullivers Sports Travel or from the WRU directly.
"Our ticketing terms and conditions are clear," said a WRU spokesperson.
"If these terms and conditions are breached then we will take appropriate action to ensure that our revenue and investment into Welsh rugby is protected.
"We also want to ensure that purchasing tickets for WRU events is a safe and secure process for supporters, with officially appointed partners who invest year on year at all levels of the game.
"Our advice to our supporters is loud and clear: please always 'buy official' as tickets purchased from non-official sources cannot be guaranteed."
WRU official Offsite Hospitality Operator Events International is the only officially sanctioned ticket source for off-site hospitality packages. Onsite hospitality at Principality Stadium is offered directly by the WRU itself.
The WRU's Official Travel Partner Gullivers Sports Travel is the only company able to offer travel packages which include match tickets.
It is against the WRU's ticket terms and conditions to re-sell tickets above face value anywhere else other than via its officially licensed secondary market website, Seatwave - where only certain parties including member clubs are able to re-sell and limitations apply. Seatwave is contractually obliged to comply with measures which protect consumers, with the WRU verifying all WRU tickets sold under this arrangement through a robust checking process.
Any supporters who have purchased tickets for any WRU events and are concerned about their validity should contact the WRU via unofficialticketing@wru.wales as soon as possible.