The public has 60 days to dispute the fee increase, and according to a memo penned by National Park Service Director, Jonathan Jarvis, "If there is significant public controversy, a park may choose not to implement... fees." However, a park "may phase in the new rates over three years, or delay the new rates until 2016 or 2017." So, there you go: your voice will be heard.
Good news, though, if they do move ahead with the price hike. The Grand Canyon, which last raised entry fees in 1997, is one of 10 parks including Yellowstone, Yosemite, and Zion that's limited to a maximum fee cap -- $15 per person and $30 per vehicle. So, unless somebody changes the rules (and, like, that never happens in Washington), this is as high as fees should climb in the foreseeable future.