According to the IRS regulations, if the employer employers 250 or more employees, the employer MUST submit the ACA reporting electronically.  The IRS publishes and presents extensive documentation and webinars on the technical aspect of transmitting ACA reporting data to the IRS (dubbed AIR – Affordable Care Act Information Returns).

For further information, click here: https://www.irs.gov/e-file-providers/air/affordable-care-act-information-returns-schemas