Since January 1, 2012, any tax return preparer who anticipates preparing and filing 11 or more Forms 1040, 1040A, 1040EZ and 1041 during a calendar year generally must use IRS e-file (unless the preparer or a particular return is administratively exempt from the e-file requirement or the return is filed by a preparer with an approved hardship waiver).
Members of firms must count returns in the aggregate. If the number of applicable income tax returns is 11 or more, then all members of the firm generally must e-file the returns they prepare and file. This is true even if a member expects to prepare and file fewer than 11 returns on an individual basis.
IRS refers to preparers who are subject to the e-file requirement as "specified tax return preparers." See IRS.gov for additional information and frequently asked questions.