A council planning to auction an LS Lowry painting to help balance its books may be excluded from the Museums Association, its chief has said.
A Riverbank was bought in 1951 by Bury Council in Greater Manchester for £175, but could now fetch up to £500,000.
Mark Taylor, director of the Museums Association, described the sale as "deeply irresponsible" and said it faced disciplinary action.
The authority said it was putting its people before a picture.
The painting has been removed from display at Bury Museum and Art Gallery to prepare it for sale at Christie's on 17 November.
"It really is deeply irresponsible of Bury to start flogging off some of their pictures," said Mr Taylor.
"Museums are very much about people's identity and of course Lowry was one of the great artists of North West England.
"It's really important the children, and people of all ages who go there, understand about the history of Bury and for them just simply to sell this picture for short term reasons, future generations will never see it and the picture may well leave the country."
Mr Taylor told BBC Radio 4's Today programme that he still hoped to convince the council to keep the artwork.
But he said disciplinary proceedings had been set up should the sale go ahead and expulsion was one of the options open to the panel.
"If that happens we will encourage governments and public funding bodies to refuse to deal or give any money to Bury museums," he said.
But Bury Council leader Wayne Campbell told the BBC the association's statement showed "a level of ignorance unsurpassed in the debate".
He said the association had never had to make "the real decisions faced by a poorly funded public authority, anxious to ensure its spending was directed to vulnerable children, as Bury had to face in 2005/06".
"They don't live in the real world," said Mr Campbell.
"Here in Bury we have decided that people come before a picture, and that can only be right.
"I am really glad this group doesn't run our social services."
'Lack of funding'
Only one authority, Derbyshire County Council, has been expelled since the association was founded in 1889.
As a result, the authority "spent a number of years in the wilderness and suffered considerably from a lack of support and funding", Mr Taylor said.
The Museums Association is a professional body which looks after the interests of museums, galleries and their employees.
LS Lowry is most famous for his matchstick men and industrial landscapes, based largely on Manchester and Salford.