The National Park Service is clashing with a landowner at the site of the Flight 93 crash over a cash donation box he installed there that relatives of Sept. 11 victims say is an insult to their memories.

The Park Service placed a black plastic trash bag over the box Wednesday, and sent Mike Svonavec a letter asking him to remove it by Friday. Svonavec owns 273 acres of the 1,300 acres east of Pittsburgh in Shanksville, Pa., where a $58 million permanent memorial and national park are planned.

"I have no intentions of removing the box from my property," Svonavec said Thursday. "My only plans are to try to cooperate with the Park Service with regard to the sale of the property."

Svonavec said he installed the donation box Saturday to cover security costs. He said that he has been paying a private security company about $10,000 a month since federal funding ran out in February, and that the site has incurred other costs, such as taxes and canceled leases.

The Park Service has a contract with Svonavec to use the land.

"The bottom line is we feel the National Park Service can't effectively carry out our mission without exercising the exclusive use and control of the site as provided for in our agreement with the property owners," Flight 93 Memorial Superintendent Joanne Hanley told the Daily American of Somerset.

Of the decision to cover the box, Svonavec said: "It's just unbelievable to my mind that that's the direction they would take, taking control of the property like a guest would at your house."

Donna Glessner, one of 43 volunteers who guide visitors at the site, said that visitors were being advised about the donation box, but that some people had placed money in it without realizing it would go to Svonavec.

"They're alarmed that they may have given their money to something that they didn't want to give their money to," she said.

Victims' families are angry not only because of the box, but also because they said Svonavec had sought $10 million for his Somerset County property.

Svonavec denied he was seeking that amount. He said that he had discussed the property with the National Park Service, and that he had rejected an earlier offer by the service based on an internal appraisal. An independent appraisal is under way, he said.

Patrick White, vice president of Families of Flight 93, said Svonavec told him last year that he was seeking $10 million. "I am not going to dignify his denials," he said.

Flight 93 was en route from Newark, N.J., to San Francisco when four terrorists hijacked it Sept. 11, 2001, likely with the goal of crashing into the White House or the Capitol. The plane crashed in a field after passengers apparently rushed the cockpit. All 33 passengers, seven crew members and the hijackers died.

The crash site is surrounded by a chain link fence that has become a shrine to the victims, with visitors leaving hats, American flags, plaques and other items.

Construction of the permanent memorial is tentatively slated to begin in late 2008 or early 2009, but fundraising has fallen well short of organizers' goals. Memorial planners have purchased only 60 acres of the site so far. Svonavec owns the second-largest parcel of land in the area after PBS Coals Inc., which owns 864 acres.