Retirement plan sponsors requesting an IRS determination letter can submit the application electronically on Pay.gov starting June 1, one month before e-filing becomes mandatory. Sponsors may still file the entire application — including Form 5300, Application for Determination for Employee Benefit Plan, any required attachments and the user fee — on paper through the end of June. IRS will return any paper applications or checks submitted after June 30. Rev. Proc. 2022-4 sets out the plans eligible to request determination letters and applicable procedures.