The list of essential service providers was published on Saturday the 28th of March 2020.
Refer to the guidance https://www.gov.ie/en/publication/dfeb8f-list-of-essential-service-providers-under-new-public-health-guidelin/ to decide whether your organisation is providing an essential service; it is not necessary to seek official authorisation if you are providing an essential service, you should identify those employees (including sub-contractors and so on) who are essential to the provision of that service and notify them. This can be done by category of employee or by individual; it could include all employees of the organisation
Note: Essential workers should carry with them their work ID, a letter from their employer confirming their essential status and 1 other form of ID.