This excerpt taken from the MCK DEF 14A filed Jun 13, 2007.
Amendment and Termination
The Board of Directors may amend the ESPP in any respect. However, an amendment that increases the number of shares reserved under the ESPP (other than adjustments upon changes in capitalization or a corporate transaction) or changes in the designation of corporations whose employees may be eligible to participate in the ESPP, other than a parent or subsidiary corporation, requires stockholder approval.
The ESPP will terminate when the number of shares available for issuance under the ESPP has been substantially exhausted, or at any earlier time by action of the Board.