Faced with hefty operating costs, the foundation building the 9/11 museum at the World Trade Centre has decided to charge an admission fee of up to 25 dollars (£16) when the site opens next year.
The exact cost of the compulsory fee has not yet been decided. Entry to the memorial plaza with its twin reflecting pools will still be free.
The decision to charge for the underground museum housing relics of the September 11, 2001 terrorist attacks has been greeted with dismay by some relatives of victims.
"People are coming to pay their respects and for different reasons," said Janice Testa of Valley Stream, whose firefighter brother Henry Miller died at the twin towers. "It shouldn't be a place where you go and see works of art. It should more be like a memorial place like a church that there's no entry fee." She was visiting the memorial with relatives from Florida.
The memorial plaza opened in 2011 on the 10th anniversary of the terror attacks, but disputes over funding have pushed the museum's opening back to spring 2014.
With the cost of operating the memorial and museum projected to be 60 million dollars (£39 million) a year, the memorial foundation voted at its board meeting last week to charge a mandatory admission fee for the museum.
"This is something that is going to be important and is going to be worth the expenditure," Joseph Daniels, president of the National September 11 Memorial and Museum, said.
He said the museum will be free during certain hours every week and will offer student and senior discounts. Foundation officials had considered an optional donation but rejected the idea.
Debra Burlingame, a foundation board member whose brother was the pilot of one of the hijacked planes, said the trade centre site is expensive to build on and to protect.
"The World Trade Centre site remains a target of interest among terrorists, so the security has to be robust and relentless," she said. "Would we like to be able to say this is free? Absolutely." But she called it "irresponsible to hope that year after year we have donations that will cover an expense like security".