Under council proposals, the 75 schools could have funding taken away for one hour of lunch staff per day, amounting to £2,200 a year each, according to figures obtained by Plaid Cymru.
Plaid said costs could be passed on to parents - which is denied by the council.
Caerphilly said it was one proposal as part of a drive to save £9m in 2016/17.
A spokeswoman said "extensive consultation" had taken place with head teachers, adding: "There is certainly no intention that any financial impact would be passed onto parents, or that the service would cease to be provided by schools."
The Labour-run authority said it was committed to spending an extra £1.9m on county borough schools in 2016.17.
A cabinet report set to be discussed next week says the 75 schools may decide to use their lunch-time supervisor to undertake the cleaning task.
However, if this happened, 75 posts (working on average one hour per day) would be withdrawn in "a worst case scenario".
This would amount to 375 hours of cleaning lost across all schools per week and the work would be shared among the remaining staff.
Plaid Cymru said the proposal would save the council £175,000 a year, which equated to around £2,200 being passed onto each school.
It added that it would be based on how many pupils eat sandwiches.
The party's candidate for Caerphilly in the assembly elections Lindsay Whittle said many parents give their children sandwiches as they cannot afford meals.
"It seems likely that this charge will be passed on to parents by many schools or pupils even banned from bringing lunches in," he added.
But the council's cabinet member for education Rhianon Passmore said the suggestion was "disingenuous and misleading", saying Plaid was "scaremongering".
"Sadly, such claims will undoubtedly cause extra worry and stress for hard pressed parents and their children.  This is wrong," she added.
Primary schools in Caerphilly county could lose money for cleaning up after children who bring sandwiches in.