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However, if this happened, 75 posts (working on average one hour per day) would be withdrawn in "a worst case scenario".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.

The Conservative-led authority made the announcement as part of plans to save Â£55m during 2011-12.
The council, which has nearly 15,000 employees, plans to save Â£7m by cutting senior management, freezing recruitment and renegotiating contracts.
Liberal Democrat councillor Keith House said the council was in "financial chaos" after it failed to plan ahead.
The Winchester-based council employs about 40,000 people.
Excluding teaching staff, who will not be affected, there are 14,990 people in 11,182 full-time posts.
The cuts represent about 8% of the workforce.
It has blamed the cuts on a reduction of Â£30.9m (14.3%) in its government grant, following the Spending Review.
Peter Terry, of public sector Unison, called the cuts "unnecessary" and said strike action could not be ruled out.
"It's quite devastating news for us, for the staff who work for the county council and for the communities that rely on the council's services," he said.
"This council has decided upon itself to roll out four years of cuts into two.
"It's a double whammy and has been made twice as bad for the people of Hampshire."
Mr House, leader of the council's opposition, said it was "unrealistic" for the council to blame the coalition government
"It should have been obvious to the council leadership way before the election that there would be some devastating times ahead," he added.
"They should have planned ahead.
"Residents are going to see that some services are going to stop and others will get worse, across the country, month by month, more and more will change."
Jane Frankum, the council's only Labour councillor, said the authority had chosen to "cut deeper and faster" than was really needed.
Council leader Ken Thornber told the BBC he expected "anxious months" of talks with unions.
He reassured residents budgets for child protection, highways maintenance and schools will be protected.
Council tax will also be frozen at last year's levels.
"One could point the finger at the last government who spent money that it was going out of style and we could point the finger at the bankers," he told the BBC.
"But quite frankly, what I have got to do is to take what the government say should be our reduction and work to it.
"I don't remember in 30 years of service anything remotely like the difficulty we are in at the moment."
The budget is expected to be approved by the full council on 24 February.
Primary schools in Caerphilly county could lose money for cleaning up after children who bring sandwiches in.
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Union bosses said 1,200 job losses at Hampshire County Council would lead to "inferior services" to communities.