Thousands of staff members at primary and secondary schools across Essex will be paid late in August due to an Essex County Council payroll error.
The council has launched a full investigation after the "internal process failure" and has written to all of those affected with a full apology.
The council believes that as many as 20,000 employees may have been affected.
Councillor Louise McKinlay, cabinet member for resources, said: "We are extremely sorry that this error happened and we have launched a full investigation to understand why it occurred and ensure it does not happen again.
"We will offer all the help, support and advice we are able to provide to affected schools employees tomorrow and will have a team standing by to deal with calls.
"Because the actual pay date for affected employees is Saturday, August 26, standing orders and direct debits due then should be processed on Tuesday after the bank holiday, but we will be able to advise schools employees with any concerns they may have."