Narrowing Exceptions for Withholding Taxes Act of 2013 - Amends the Internal Revenue Code and title II (Old-Age, Survivors, and Disability Insurance Benefits) of the Social Security Act to require a shareholder of a subchapter S corporation engaged in a professional service business to include all items of income or loss attributable to such business in determining such shareholder's net earnings from self-employment for purposes of computing employment tax liability.
Defines a "professional service business" as any trade or business substantially all of the activities of which involve providing services in the fields of health, law, lobbying, engineering, architecture, accounting, actuarial science, performing arts, consulting, athletics, investment advice or management, or brokerage services.