NEW YORK (AP) -- Strikers at the Museum of Modern Art drew support this week from celebrities, including artists Robert Rauschenberg and Art Spiegelman, filmmakers Steven Spielberg and Martin Scorsese and performers Laurie Anderson and David Byrne.

The first strike in 27 years by museum employees -- including archivists, conservators, curators, librarians and other professionals -- has dragged on for more than three months. It's the longest strike in the museum's history, yet neither side seems willing to budge and each accuses the other of bargaining in bad faith.

Points of contention include salaries as well as union demands for compulsory membership of professional staff.

The artists' names were listed under a brief open letter published in The Village Voice and Time Out New York this week asking the public to respect the picket line in front of the museum and expressing concern with what they called MoMA's refusal to negotiate. A total of 131 names appear in the letter.

Reached by phone on Wednesday, Spiegelman, the Pulitzer Prize-winning New Yorker illustrator, said he had signed the letter partly because a work of his would soon go on display at MoMA.

"I'm very upset. I'm going to feel very awkward if I have to cross a picket line to see my work," he said.

Other signers include filmmaker Pedro Almodovar, performing artist Bill T. Jones, writers John Ashbery and Susan Sontag, filmmakers Quentin Tarantino and Bertrand Tavernier and jazz musician John Zorn.

The president of the union did not immediately return calls Wednesday seeking comment, but MoMA lawyer Robert Batterman said the letter stems from a false assumption that the museum has refused to negotiate.

"There were nine months of negotiations before the strike began and numerous conversations through the mediators. I think signing such an open letter based on the unilateral representation of the union is inappropriate and will be recognized as such for people of good faith who read it carefully," he said.

The Professional and Administrative Staff Association, Local 2110 of the United Auto Workers union, started the strike on April 28 after working for six months without a contract. There have been no face-to-face negotiations since April 27 and none are scheduled.

The union represents 255 of the 650 museum employees.