Sotheby’s said it filed its claim in London's High Court against Mark Weiss Limited and business partner Fairlight Art Ventures.
The Hals painting, Portrait of a Gentleman, was supplied to Sotheby’s by Weiss. But it is thought to have been previously owned by Frenchman Giulano Ruffini who has now been linked to a number of paintings that have had their attribution questioned.
In a statement Sotheby’s said it has completed “in-depth technical analysis which established that the work was undoubtedly a forgery”. Last year Sotheby’s reimbursed the US buyer of the Portrait of a Gentleman who had paid $10m in a private deal brokered in 2011.
A statement from Weiss said that when the sale of the painting was made in 2011 it was "widely believed by all the leading connoisseurs to be a work by Frans Hals". Weiss and his advisors argue further testing should be carried out "before the assertion that this work is a modern fake can be definitively made".
The statement said Sotheby’s has "repeatedly refused to allow Weiss’s experts access to the painting to carry out the further tests."
However Sotheby's said the painting was with the "experts Mr. Weiss had instructed for a four month period and was subject to extensive testing by them. Mr. Weiss later suggested that additional tests be conducted by a new group of conservators, but Sotheby’s concluded that none of these further tests would change its conclusion”.
The Weiss statement said he "intends to contest the claim vigorously".