Officials say they've seen a huge increase in the number of people scalping reservations for campsites. A park spokesman said officials are becoming more aggressive as they try to curb scalpers.
The reservations usually sell for $20 a night, but they're being resold on sites like Craigslist for five times the face value. The nation's third-most visited park has only 900 reserved campsites available at any given time.
Scalpers are also selling permits to climb Yosemite's famous Half Dome, which the park essentially issues for free.
Officials say it appears that some scalpers may have devised ways of jumping the reservation queue, possibly through automated computer programs that can instantly snag cancellations.
The Associated Press contributed to this report.