On days of projected high attendance, Annual Passport holders and Disney Cast Members and Employees may be required to obtain handstamps. This is to help prove, along with the Ticket Entries that they are re-entering the park for that day, as opposed to first time entry.
As part of it's crowd control measures, the
Disneyland Resort does reserve the right to close off entry to the Theme Parks to first time entry at any time, and only admit those Guests who are re-entering.