From SCOTUblog: "The critical detail is that you cannot take away the existing Medicaid funds"

http://www.scotusblog.com/cover-it-live/

"Nothing in our opinion precludes Congress from offering funds under the ACA to expand the availability of health care, and requiring that states accepting such funds comply with the conditions on their use. What Congress is not free to do is to penalize States that choose not to participate in that new program by taking away their existing Medicaid funding." (p. 55)