Washington (CNN) Nine members of the National Park System Advisory Board quit Tuesday, citing concern over the Trump administration's priorities regarding the national parks, according to a letter obtained by CNN.

The letter, sent by nine members of the board to Interior Secretary Ryan Zinke, says the group has been unable to meet with Zinke and the Interior Department during his first year in the position.

The author of the letter, former Alaska Democratic Gov. Tony Knowles, said the board is supposed to meet twice a year. However, he said, he's been told things were "suspended."

Previous administrations met with the board immediately, Knowles noted, having served on the board for seven years.

A request for comment has not been returned by the Interior Department.

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