A spouse or additional owner may participate in the plan as long as he or she is on the company’s payroll and meets the plan’s eligibility requirements. Employees other than a spouse or additional owner are not allowed in the TRA Solo(k) Plan. However, the TRA Solo(k) Plan may be used if a business has employees that can be excluded from the plan. The following types of employees may be excluded: Employees who are under 21 years of age. Employees who work less than 1,000 hours per year. The following types of employees are automatically excluded: Employees who belong to a collectively bargained unit (union). Employees who are nonresident aliens and receive no U.S. income.