UPDATED 11.52am: A union is considering legal action, as Southern District Health Board moves to privatise its food services.

Hospital patients in Otago and Southland will be eating meals made with ingredients sourced from around the country that are fresh, pre-prepared and frozen ingredients - options that the DHB are assuring is not a change from the current meal structure.

The meals will be driven from Auckland, and patient meals will be prepared on site with ingredients from around the country.

Food and Service Workers Union organiser Anna Huffstutler says a decision will be made within the next week or so, over whether to take legal action.

It's part of a plan to reduce a financial deficit that could reach more than $40 million next year.

The DHB believes it could save nearly $7.5 million over four years.