In a Lancashire County Council document seen by the Lancaster Guardian, schools have been told to be prepared to offer "a short-term packed lunch type menu", or possibly "a longer-term simplified menu offering" but are warned that "both options may be required".
And parents at some schools have already been told that a temporary menu has been introduced due to low food stocks and limited deliveries.
The shortages are expected throughout Lancashire County Council's schools as supply chains face pressure throughout the country.
Lancashire County Council said it was looking at bringing in a temporary menu in October to help restock, so that things can go back to normal after half-term.
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The council operates two menus a year to reflect available fresh produce, which are well advertised in advanced to help provide certainty due to being such a large authority - preparing 65,000 meals a day.
The information, issued to schools earlier this week, says: "Many will be aware of the ongoing food supply disruptions and the impact this is having on the availability of published menu items.
"It is important to note that these impacts are not unique to the school meals sector and nor are they isolated to Lancashire.
"Supermarkets, fast food outlets and the hospitality industry are all encountering similar nationwide difficulties, as are other sectors outside of the food supply chain.
"The national shortage of workers within the food industry sector, namely heavy goods vehicle drivers, butchers, food producers and warehouse staff, continues to have a profound effect upon the whole supply chain.
"This situation is likely to be further exacerbated by the reported shortage of CO2 which is expected to impact the humane slaughter of animals, food packaging processes and food shelf life.
"Preparations for the forthcoming Christmas period will also add significant strain to an industry which is already struggling to cope with demand."
The document continues by saying the council's catering service is working with colleagues to identify suitable contingency arrangements which would assist with improvements to food supply disruptions.
However, they admit that "this is proving difficult at a time when the whole food sector is encountering the same effects as ourselves" and say a changed menu is likely if they are unable to identify suitable contingency arrangements.
"This may be a short-term packed lunch type menu, which would allow for the reduction in normal delivery volumes whilst stores are replenished, a longer-term simplified menu offering, or both options may be required," they say.
"Further communications will be shared with schools' once communications with contingency suppliers have concluded and decisions have been made.
"In the meantime, colleagues are thanked for their patience and understanding in these unprecedented times."
A council spokesman said there have been no instances of children not receiving a school meal and nor is this considered a risk.
County Coun Jayne Rear, cabinet member for education and skills, said: "As has been widely reported in the media, nationally there have been issues with food supply chains caused by a shortage of delivery drivers and food industry workers.
"We are working hard to minimise the effect on our schools, but in some instances we may need to offer a reduced menu compared to our usual large choice of dishes."
Sam-Ud-din, Lancaster & Morecambe District Secretary for the National Education Union, said: "This may be un-precedented, but not unpredictable. Yet another example of lack of foresight and sufficient planning by a government that avoids its responsibilities for ensuring that energy supplies are sufficiently robust to withstand the impact of Brexit, disputes with countries that we rely on to share scarce resources and just one, albeit large, cable being destroyed in one fire. And yet again, it's our children that suffer."