Massachusetts Attorney General Maura Healey wants the state appeals court to block temporarily the auction of art owned by the Berkshire Museum.
The first batch of art -- including a pair of Norman Rockwell paintings the artist himself donated to the museum -- is scheduled for sale Monday at Sotheby's in New York.
Museum officials have said the proceeds will stabilize its finances and fund a major renovation.
Superior Court Judge John Agostini this week denied a request from Healey and other plaintiffs to stop the sale.
In its appeal filed Friday, the AG's office said Agostini "abuse[d] [his] discretion through clear errors of law." And it questioned why the auction has to happen now, before the legal fight is exhausted.
"If these objects are sold, there likely will be little if any opportunity to get them back," the AG wrote. "There is no indication that the museum is in immediate financial crisis."
The museum's lawyer, William F. Lee, issued a statement calling the attorney general's appeal "misguided."
"Continuing this litigation jeopardizes vital educational, cultural and economic resources in a struggling community, placing the special interests of a portion of the well-funded arts community over people, especially young people, really in need," the statement read.
New England Public Radio's Adam Frenier contributed to this report.