John Chamberlain, Candy Andy (1963), painted and chromium-plated steel, 37 by 31½ by 27 inches.

A June 28 letter to Dia Art Foundation director Philippe Vergne from Paul Winkler, brother of Dia co-founder Helen Winkler, opposing the foundation's planned sale of artworks this fall at Sotheby's, has become public.

"To sell art works at the core of the ideas and collections of Dia is an outrage and to do so for the purpose of acquiring works by other artists is counter to the unique vision and spirit of Dia," Winkler wrote in the letter, which was published by Tyler Green at his Modern Art Notes blog today.

The sale of 27 works is to include works by John Chamberlain, Cy Twombly and Barnett Newman, and is expected to bring in excess of $20 million.

Neither Winkler nor representatives of Dia Could be immediately reached for comment.