Professional Employer Organization Workers Benefits Act of 1999

Professional Employer Organization Workers Benefits Act of 1999 - Amends the Internal Revenue Code (IRC) to provide that, for purposes of the taxes imposed by subtitle C (Employment Taxes), a certified professional employer organization shall be treated as the employer (and no other person shall be treated as the employer) of any work site employee performing services for any customer of such organization, but only with respect to remuneration remitted by such organization to such work site employee and exemptions and exclusions which would otherwise apply shall apply with respect to such taxes imposed on such remuneration. Sets forth provisions concerning: (1) secondary customer liability for employment taxes; (2) liability with respect to individuals purported to be work site employees; and (3) special rules for related parties.

Amends IRC definition provisions of subchapter D (Deferred Compensation, Etc.) of subtitle A (Income Taxes) to provide that, subject to exceptions, if a certified professional employer organization establishes or maintains a plan to provide employee benefits to work site employees, then, for purposes of applying the provisions of this title applicable to such benefits: (1) such plan shall be treated as a single employer plan established and maintained by the organization; (2) the organization shall be treated as the employer of the work site employees eligible to participate in the plan; and (3) the portion of such plan covering work site employees shall not be taken into account in applying such provisions to the remaining portion of such plan or to any other plan providing employee benefits (other than to work site employees).

Defines "certified professional employer organization" and "work site employee."

Sets forth provisions concerning, among other things: (1) employer aggregation rules; (2) determination of employment status; and (3) reporting requirements.