The National Park Service may limit the number of items it gathers from the Vietnam Veterans Memorial, reported The Associated Press. The department plans to keep only items associated with veterans listed on the memorial.

"By refining the scope of the Vietnam Veterans Memorial Collection, we can ensure that our energy and resources will preserve items with a direct and specific relationship to veterans of the Vietnam War," Gay Vietzke, superintendent of the National Mall and Memorial Parks, told Reuters.

According to Statista, around four million people visit the monument every year.

The park service has been collecting items left at the monument since 1982, reported PBS. It stores them in the Museum Resource Center in Washington D.C. Over the years, the department has collected over 500,000 items from the Vietnam Veterans Memorial, including a customized Harley-Davidson motorcycle, military decorations and thousands of personal notes.

"It really is a very unique collection – and a vast majority of these items are left anonymously," Bob Sonderman, director and regional curator of the Museum Resource Center, said in an interview with the news organization.

The Vietnam Veterans Memorial Fund is currently raising funds to build a new storage facility for the items. The space, called The Education Center at The Wall, will cost over $100 million. According to its architects, the building will not only showcase some of the items but also contain portraits for each of the more than 58,000 combat veterans memorialized on the Vietnam monument and an interactive timeline of the war.

In August of last year, the National Park Service also created a virtual collection of 500 items left behind at the memorial.

The park service is now accepting public comments on the proposed changes to its item-collection policy. The deadline is March 10.