may, but need not, exclude an employee from an automatic contribution plan maintained by the employer until the first day of the second calendar month beginning on or after the day the individual begins work for the employer. (v) Seasonal or temporary employees The employer may, but need not, exclude an employee from an automatic contribution plan maintained by the employer to the extent that such employee is not expected to work during more than three months during the 12-month period starting when such employee would otherwise be required to be eligible under such plan. (C) Special rules for controlled groups Eligible employees within an employer need not be eligible to participate in the same automatic contribution plan. For purposes of this subsection, the term employer shall include all employers treated as a single employer under subsection (b), (c), (m), or (o) of section 414. (D) Special rules for grandfathered plans This paragraph shall not apply to a plan described in paragraph (2)(D) until the sixth plan year beginning on or after the date of enactment of the Automatic Retirement Plan Act of 2017 . In the case of an eligible employer (as defined in section 408(p)(2)(C)(i)), eighth shall be substituted for sixth in the preceding sentence. (4) Investment requirements Except in the case of a plan that is an automatic contribution plan by reason of paragraph (2)(D), any investment made in the absence of an investment election by a participant or beneficiary shall be invested in accordance with regulations prescribed by the Secretary of Labor under section 404(c)(5) of the Employee Retirement Income Security Act of 1974. (5) Lifetime income requirements Except in the case of a plan that is an automatic contribution plan by reason of paragraph (2)(D), the lifetime income requirements described in this paragraph are— (A) Guaranteed income for life available A plan shall not be treated as an automatic contribution plan unless the plan permits participants to elect to receive at least 50 percent of their