The Andy Warhol Foundation for the Visual Arts is threatening to stop its financial support of Smithsonian exhibitions if the institution does not restore a work of art that was removed from a current show following attacks by the president of the Catholic League and two Republican Congressmen. The Warhol Foundation gave $100,000 to the Smithsonian for the exhibition, “Hide/ Seek: Difference and Desire in American Portraiture,” at the National Portrait Gallery in Washington, one of the Smithsonian museums. The work was removed on Nov. 30.

In a letter sent on Monday by e-mail and FedEx to G. Wayne Clough, the secretary of the Smithsonian, Joel Wachs, the president of the Warhol foundation, said the board had voted unanimously Friday to demand that the Smithsonian reinstate the work, an excerpt of a video by the artist David Wojnarowicz, or the foundation would not finance any future Smithsonian shows.

“I regret that you have put us in this position, but there is no other course we can take,” Mr. Wachs wrote in the letter, which the foundation also sent to the news media. “For the arts to flourish, the arts must be free, and the decision to censor this important work is in stark opposition to our mission to defend freedom of expression wherever and whenever it is under attack.”

On Monday afternoon Mr. Clough said through a spokeswoman, “While we regret the foundation’s action, the Smithsonian’s decision to remove the video was a difficult one, and we stand by it.”