Southern Railway is coming under increasing pressure to reconsider controversial changes to its timetable amid fears of the "devastating" impact on rail travellers.
Kent County Council (KCC) said parents and schoolchildren will be among those badly affected by the decision to cut 341 trains a day in a revised timetable for a month.
And, in a withering letter to the company on Wednesday, the Conservative-led authority said Southern's changes will have a "devastating" impact on other people heavily reliant on rail travel.
KCC's transport councillor Matthew Balfour made the council's robust views plain about the "appalling level of service" in a letter to Southern's chief executive Charles Horton.
He said: "The proposed emergency timetable will not help at all those parents and pupils who desperately need to access their places of education.
"I trust that your company will reconsider the emergency timetable, which will have a devastating effect on those for whom travel by rail is the only viable and realistic option for their essential journeys."
Southern has come under fire for its handling of its train services in parts of London, East and West Sussex, Surrey and areas of Kent and Hampshire.
Some passengers have lost their jobs because of delays to their trains, the Transport Select Committee heard this week.
And MPs have been contacted by travellers angry at not getting home to see their children because of delays and cancellations.
The disruption has been caused by staff shortages and industrial action.
But the firm said it was pressing ahead with changing the role of conductors in August, the issue which has sparked a series of strikes by members of the Rail, Maritime and Transport (RMT) union.
Southern chief executive Charles Horton has apologised to passengers but said the cancellations from next Monday, amounting to 15% of its services, would deliver a more "resilient" level of services.
The operator said it was also taking action to "encourage staff back to work" and was working with the Government to introduce more generous passenger compensation.
Changes include the suspension of Southern's West London Line services between Milton Keynes and Clapham Junction, reductions in service on the Coastway routes, buses replacing most trains between Seaford and Lewes, and a reduced off-peak service between Tonbridge and Redhill where passengers for London Victoria will need to change trains.
Paul Plummer, chief executive of the Rail Delivery Group, which represents train operators and Network Rail, said: "Decisions to cancel trains are never taken lightly and only when there is no alternative or to avoid causing greater disruption. We will never compromise on safety.
"In 20 years, passenger numbers have doubled and thousands more trains run every day, meaning that the railway is now full in many places.
"The challenges facing the rail industry today - modernising services, improving efficiency and operating trains during major improvement work, for example at London Bridge station - stem from decades of under-investment."
He said billions were being spent to deliver better railway services.