it's really unprofessional to present the act of quitting as requiring 2 weeks' notice
If it's part of the contract then it's not unprofessional at all to bring up the terms that you've agreed on. My job requires a month's notice and it wouldn't be unprofessional for my employer to bring that up if I tried to quit on the spot.
That being said, I don't live in a place with "at-will employment", which is a fucking travesty and should never have been allowed in the first place.