A Section 125 “Cafeteria Plan” is a written document maintained by an employer where the participants of the plan can receive benefits on a pre-tax basis via salary reduction.
You can read more information detailed in this Lively blog post.
As an employer offering an HSA to your employees, you are required by the IRS to have a Section 125 plan on file ready to be presented should it be requested for an IRS audit or directly by one of your employees.
If you are looking for a resource to help you put a Section 125 plan in place we recommend Core Documents.
Please consult a tax professional for specific questions regarding your company and the Section 125 plan.