(CNN) -- The leader of a group representing 9/11 victims' families on Friday criticized the National September 11 Memorial Museum's decision to charge a $24 admission for visitors when it opens this spring.
"It was never intended to be a revenue-generating tourist attraction with a prohibitive budget and entrance fee," Sally Regenhard, assistant chairwoman of the group 9/11 Parents and Families of Firefighters and World Trade Center Victims, said in a prepared statement.
She calls on government officials "to stop this outrageous fee and bring costs under control."
"The rich will visit the museum, but the poor and middle-class families won't be able to afford it," she said.
But the ticket price, which was approved Thursday, will "ensure the organization's financial health" and "help fund the necessary operational costs," said a statement from Joe Daniels, the 9/11 memorial president.
And the fee will help balance a $63 million operating budget for 2014, said Anthony Guido, communications manager at the 9/11 memorial.
"The 9/11 Memorial does not yet receive government support for ongoing operations as many other important museums of our national history do," Daniels said.
The memorial is seeking federal funding which would enable the expansion of education programming, Guido said.
Relatives of 9/11 victims are exempt from all fees and charges. Discounts will be offered to students, seniors and other groups, and the museum will offer free general admission between 5 and 8 p.m. each Tuesday.
New York Mayor Bill de Blasio spoke out against charging an admission fee Wednesday.
"This is a nationally important site. It's something that people come to from all over the country, all over the world, and we need the federal government to join with us," he said.
The underground museum at the World Trade Center is scheduled to open in mid-May. The above-ground memorial plaza, which has had 11.5 million visitors since opening two years ago, will continue to be free.
The memorial preserves the history of September 11, 2001.
"The stories and the lives of the nearly 3,000 innocent people lost that day will be forever honored at the Museum through artifacts, exhibitions and first-person accounts," Daniels said.
CNN's Lorenzo Ferrigno contributed to this report.