The Warehouse is in the sin bin after the Waikato Rugby Union discovered stores selling "counterfeit" Mooloo scarfs.
The red, yellow and black colours have been worn by Waikato since 1929 and were trademarked in 1995.
Union marketing manager Pat Mellsop said The Warehouse had not been awareof the trademark until the union blew the whistle on them.
"They were pretty good, they took them down.
"They were not trying to be deceptive, obviously they thought it was kosher."
Mr Mellsop said he was unaware of any other major rugby union in the country, apart from the All Blacks, holding a similar trademark.
"Weve got the advantage of three colours which makes it easier. It's so distinctive. It's a bit tougher (for teams) with only two colours."
The Warehouse was not the first to sell knock-off supporters gear. Mr Mellsop said it was a regular occurrence with sellers peddling everything from socks to scarfs.
Cash from official merchandise sales goes to the union and back into rugby.
"Its a pretty important income. Which is why we wanted to get the word out, to warn people, particularly now that we are the Ranfurly Shield holders: Don't try to make money off our back and not put it back into rugby because you can't have the defence now that you are unaware."
The discovery came a time when the Waikato rugby brand is flying high. Fans have already snapped up 16,000 tickets for Waikato's first shield defence against Canterbury this weekend and supporters gear was flying out of official retailers' doors, Mr Mellsop said.
The club also intends to use a run of scarfs to raise funds for Hospice Waikato.
The Warehouse said it had sold only a small number of the $12.90 scarfs.
