New York Codes, Rules and Regulations
Title 20 - DEPARTMENT OF TAXATION AND FINANCE
Chapter II - Income Taxes and Estate Taxes
Subchapter A - New York State Personal Income Tax Under Article 22 Of The Tax Law
Article 5 - Withholding of New York State Personal Income Tax
Part 171 - Requirement Of Withholding New York State Personal Income Tax From Wages
Section 171.2 - Definition of employer

An employer is any person or organization qualifying as an employer for Federal income tax withholding purposes and maintaining an office or transacting business within New York State, whether or not a paying agency is maintained within New York State. (See also Part 177 of this Article with respect to designation of third parties to perform acts required of employers.)