All service contracts shall include a clause requiring the bidder or offeror, in order to be considered a responsible bidder or offeror for the purposes of this Code, to certify to the purchasing agency (i) that it shall offer to assume the collective bargaining obligations of the prior employer, including any existing collective bargaining agreement with the bargaining representative of any existing collective bargaining unit or units performing substantially similar work to the services covered by the contract subject to its bid or offer, and (ii) that it shall offer employment to all employees currently employed in any existing bargaining unit performing substantially similar work that will be performed by the successor vendor.
     This Section does not apply to heating and air conditioning service contracts, plumbing service contracts, and electrical service contracts.