Can a company arbitrarily enforce a non-complete agreement?

I was just laid off from an IT consulting firm where I was a full time employee for eight years. I am being asked to sign a non-compete agreement in order to gain severance. According to the terms of the non-compete agreement, for a period of eighteen months following the date of the agreement I cannot provide consulting services to any accounts in which the Employee represented the Company in the twelve months preceding the termination of employment. One of the Company's clients, for whom I did provide consulting services in the past year, has offered me a full-time job. Is a full time position considered "providing consulting services"? Additionally, the Company has allowed the client to directly hire away many of their consultants over the years. Is the Company allowed to be arbitrary in its enforcement of a non-compete agreement?