Kelly,
Did you know that the hours would change during the holiday period?
If you did, you could have just taken on the staff as seasonal employee's, that way everyone would have understood, and of course had contracts to match this scenerio.
Having said that if its a year round contract, you just change the hours worked during the season to reflect the number of hours that are required, that way your staff know that their hours will drop during high season.
Regards,
Rob