Is there any law that precludes an Ecuadorian citizen from being a partner in a US company?

Yes, for example an "S" election corporation...and there are other issues that arise for non-US citizens. By Grace... Shawn Jackson ESQ. (707) 584-4529  Business Development Attorney EMAIL: Attorneys@CaliforniaBusinessDevelopment.com www.CaliforniaBusinessDevelopmentAttorneys.com www.CaliforniaBusinessDevelopmentCenter.com www.CaliforniaBusinessDevelopmentPlans.com www.CaliforniaBusinessDevelopmentIncubator.com                 No communication resulting herein shall create an attorney-client relationship unless a separate retainer agreement is signed by attorney and client. The information provided neither is  legal advice nor is it conveyed in the course of an attorney-client relationship, but is intended merely as a general overview with regard to the subject matter covered. You should not act upon this information without seeking professional counsel such as any attorney in this office in a subsequent email communication (agreement) and the formation of an attorney client relationship.