From an email forwarded me from my NASA grant PI:
The Full-Year Continuing Appropriations Act of 2011 (P.L. 112-10), Section 1340(a), states, “None of the funds made available by this [Act] may be used for the National Aeronautics and Space Administration or the Office of Science and Technology Policy to develop, design, plan, promulgate, implement, or execute a bilateral policy, program, order, or contract of any kind to participate, collaborate, or coordinate bilaterally in any way with China or any Chinese-owned company unless such activities are specifically authorized by a law enacted after the date of enactment of this division.”
So all the projects in the NASA LCLUC Program dealing with China must be compliant with this statute.
Apparently more than one country restricts research for political reasons.