I've signed a contract with a company, but said company has not signed the contract themselves to confirm that I'll be hired (I'm going through background checks at the moment).
I have been asked to interview with another company, B. Am I acting in an unprofessional way if I accept B's offer?
I've looked at this, and it's similar but not the same.
From a legal point of view:
In a contract between two businesses, if only one side signs, parts of it may still be enforceable: http://www.avvo.com/legal-answers/is-a-contract-valid-if-only-one-of-the-two-parties-423043.html
However if you are being hired to be an employee, then in fact most of the power rests with you, not the employer. Employment law usually dramatically favours the employee not the employer. So there's really no legal problem with declining the job.
From a professionalism point of view:
Since company A has not yet said that they'll hire you, then you don't have a contract yet. You have offered to work for them, but they have not yet accepted. Offer typically have a time limit expressly or implied. If you want to display exemplary professionalism then tell Company A that they have a certain amount of time to make up their mind otherwise you are withdrawing your offer to work for them.
Because you don't have a signed offer back from Company A, you should continue to apply for other positions, and even go on interviews. Until Company A accepts your offer, you still don't have a job.
Applying for a position, and even going on interviews is not a commitment to a company. You are hedging your bets in case the expected position with company A falls apart in the next few days. Imagine if you turned down scheduling an interview, and withdrew all outstanding applications; only to get word from company A that they will not be able to start you for 90 more days because a customer has delayed the contract. You would have to re-start your job search from scratch.
Another way to look at it is to see what would happen if the contract was valid.
If they hire you and you simply don't show up, normally they won't be able to claim damages, but they will fire you pretty quickly. Depending on the country you're in and the excuses you come up with, they might still have to pay you up to a month's salary for not showing up. This is the worst case scenario for the company.
Because of this worst case scenario, a company will not enforce a contract unless the contract you signed includes no show penalties - but I can't think of any such example, except for contractors. Normally if you tell a company you want to annul an employment contract before it started, even if both parties already signed it, it's in the company's own best interest to let you go.
On the topic of professionalism: Looking out for your career is professional, although it's not always nice, and not always ethical. The people who wanted to hire you might be disappointed with your actions, and file you under "don't ever make an offer to this guy again". Anyone else won't hear about the story, and even if they do they most likely won't care.
