A business, trade, profession or occupation (as distinguished from personal services as an employee) is carried on partly within and partly without New York State when one or more of the activities described in of section 132.4(a) of this Part is systematically and regularly carried on within New York State and one or more of such activities is systematically and regularly carried on outside New York State, or when one or more of such activities is systematically and regularly carried on both within and without New York State.
N.Y. Comp. Codes R. & Regs. Tit. 20 § 132.14