An employer is usually the plan sponsor, i.e. the party that adopts the retirement plan. This includes sole-proprietorships, partnerships, corporations and non-profit organizations.
An employer typically has hirees who perform any service, of whatever nature, as an employee. A sole proprietor is treated as his or her own employer for retirement plan purposes.
A partner is not an employer for retirement plan purposes. Instead, the partnership is treated as the employer of each partner.
IRC § 414, Publication 560
Additional Helpful Information
- For employer-plan purposes, the employer can be more than one businesses, if there is a controlled group relationship or affiliated service group relationship between the businesses.