Unfortunately,technically, an employer, even one with no employees, cannot petition to decertify a union.
Only employees can petition to decertify a union, by filing a petition with the National Labor Relations Board.
However, as an owner, you can withdraw recognition of an incumbent union if it can establish either:
(i) that the union no longer enjoys majority status in fact; or
(ii) that the withdrawal is predicated on a reasonably grounded doubt as to the union’s continued majority status, which doubt was asserted in good faith, based upon objective considerations, and free of employer unfair labor practices.
Since there are no employees with the corporation currently, you can definitely assert that the union does not hold majority status.
You can request that the recognition of the union be withdrawn by contacting your local National Labor Relations Board office, which you can find here:http://www.nlrb.gov/who-we-are/regional-offices
If you are successful in doing so, the collective bargaining agreement that is in force would be invalidated and you would be able to begin business without the union.