Yes, it is valid. Directors are fiduciaries of the corporation, meaning that they bear the duty of utmost fidelity to the corporation's interests. If a conflict of interests arises, a director can recuse her/himself from discussing the issue and voting on it; but, sitting on the boards of 2 directly competing corporations, a director would have to recuse herself from all (or nearly all) decisions - in both corporations. Therefore, that person would not be able to serve either corporation as a director; and a by-law provision preventing such a situation is perfectly logical.
Answered on Jan 18th, 2013 at 1:49 AM