Dinner ladies from schools across Hackney, east London, staged an unofficial strike on Wednesday of last week.
More than 40 schools have failed to increase pay to equal the salaries paid to colleagues in other Hackney schools.
The dinner ladies work for catering contractors Sunway and are members of the T&G union.
The 18 schools where Sunway operates in Hackney are now to ballot on official strike action.
Cathy Stewart, the T&G catering staff representative, said, “Our workload has soared. Some of the kitchen assistants in the borough earn as little as £9,000 a year.
“The government say it is putting more money in but we are not seeing it in facilities or wages. All we want is fair pay. We will see how management respond to the ballot.”