NEW YORK (Reuters) -Investor Artisan Partners is unhappy with Axalta Coating Systems' ( AXTA ) plan to combine with AkzoNobel in an all-stock deal that would create a paint industry giant with an enterprise value of $25 billion, according to a letter to shareholders.

"As an Axalta shareholder, we believe the only proper response to this proposed transaction is an absolute and resounding "NO," Artisan Partners fund managers Daniel O'Keefe and Michael McKinnon wrote in a letter to Axalta shareholders, which was seen by Reuters.

The pair also said they would interested speaking with any other interested buyers.