No, there should be a clause in the contract specifying a mutual minimal time of notice for ending the employment. Also see this great post http://www.kalzumeus.com/2011/07/08/business-psychology/
I was recently creative director of a small software company that let their design team go. When I started the owner changed my employee contract from 14 to 28 days with the assumption that since I was in a management position with 5 reports, were I to leave the transition would have been hard to squeeze in to the standard 2 week period.
When he announced he was letting everyone go with 2 weeks severance, he was not too happy when I reminded him my contracted stipulated 28 days (he did honor it though).