26 CFR § 31.3401(d)-1 - Employer.
(b) It is not necessary that the services be continuing at the time the wages are paid in order that the status of employer exist. Thus, for purposes of withholding, a person for whom an individual has performed past services for which he is still receiving wages from such person is an employer.
(c) An employer may be an individual, a corporation, a partnership, a trust, an estate, a joint-stock company, an association, or a syndicate, group, pool, joint venture, or other unincorporated organization, group or entity. A trust or estate, rather than the fiduciary acting for or on behalf of the trust or estate, is generally the employer.
(d) The term employer embraces not only individuals and organizations engaged in trade or business, but organizations exempt from income tax, such as religious and charitable organizations, educational institutions, clubs, social organizations and societies, as well as the governments of the United States, the States, Territories, Puerto Rico, and the District of Columbia, including their agencies, instrumentalities, and political subdivisions.
(e) The term employer also means (except for the purpose of the definition of wages) any person paying wages on behalf of a nonresident alien individual, foreign partnership, or foreign corporation, not engaged in trade or business within the United States (including Puerto Rico as if a part of the United States).
(f) If the person for whom the services are or were performed does not have legal control of the payment of the wages for such services, the term employer means (except for the purpose of the definition of wages) the person having such control. For example, where wages, such as certain types of pensions or retired pay, are paid by a trust and the person for whom the services were performed has no legal control over the payment of such wages, the trust is the employer.
(g) The term employer also means a person making a payment of a supplemental unemployment compensation benefit which is treated under paragraph (b)(14) of § 31.3401(a)-1 as if it were wages. For example, if supplemental unemployment compensation benefits are paid from a trust which was created under the terms of a collective bargaining agreement, the trust shall generally be deemed to be the employer. However, if the person making such payment is acting solely as an agent for another person, the term employer shall mean such other person and not the person actually making the payment.
(h) It is a basic purpose to centralize in the employer the responsibility for withholding, returning, and paying the tax, and for furnishing the statements required under section 6051 and § 31.6051-1. The special definitions of the term employer in paragraphs (e), (f), and (g) of this section are designed solely to meet special or unusual situations. They are not intended as a departure from the basic purpose.