The GMB union said all hospitals, schools and meals-on-wheels services should verify that horse meat had not been served to vulnerable people.
Brian Strutton, the union's national secretary for public services, said: "Hospitals, schools and council care services provide millions of meals with meat products every week to the young, the elderly and the sick.
"With ever-tightening budgets, some of these may have turned to cheaper meat supplies and inadvertently been or still be using horse meat.
"With rising public alarm over the prevalent use of horse meat in retail food products and possible health issues, the Government must require all public services that feed vulnerable members of society to verify that they have not used horse meat."
A leading food scientist says the rule change that sparked the horsemeat beef scandal affected lamb products too, and they should be tested.
Retailers and the Food Standards Agency held an emergency meeting today to decide how to proceed with the horsemeat scandal.
The government has called an emergency meeting with retailers and the Food Standards Agency to discuss the horsemeat scandal.