It said the tickets for the sell-out match at Cardiff's Principality Stadium had been sold in breach of its terms and conditions.
The WRU said it had secured a High Court injunction preventing Evental Ltd from breaching its rules.
Ticket holders have been urged to check tickets are from authorised sources.
Terms and conditions state WRU tickets cannot be sold above face value anywhere other than its licensed secondary market website, Seatwave.
The only other official ticket sources are the WRU's sole off-site hospitality operator Events International, WRU onsite hospitality, WRU member clubs and official travel partner Gullivers Sports Travel.
The WRU said it has "made a commitment to look into the individual circumstances surrounding purchases and will do what it can to help individuals who have purchased in good faith".
The Welsh Rugby Union is cancelling around 200 tickets for Friday's Six Nations match against Ireland which were re-sold by unofficial providers.