All employees that meet minimum eligibility criteria must be included in a SEP IRA arrangement. If you decide to establish a SEP IRA, every eligible employee must be given a SEP IRA account to receive employer contributions.
An employer is able to expand eligibility but cannot ignore the minimum eligibility rules. If an employee is over 21, has worked at the business in 3 of the last 5 years, and has earned over $600 in the most recent year.
Union workers covered by union benefits do not have to be included, and neither do non-resident alien employees (those with Green Cards). If an employee does not want to set up a SEP IRA, the employer must set up a SEP IRA on their behalf.