I believe the name of the law was the NIH Revitalization Act of 1993. I'll do some more checking to make sure that's the name of the law.
In any event, it's not really necessary to find the law itself, since I believe the NIH is an independent agency, like OSHA, and is therefore not subject to direct presidential control.
NIH is not an independent agency. It is an agency under HHS. The only independent agencies under the federal govt are the CIA and the US Postal Service.