Hundreds of employees of Redcar and Cleveland Borough Council have been mistakenly told their pay is being cut.
Workers say they have been left confused and angry after a computer glitch and errors in information following a pay review.
However, council chief executive Colin Moore assured them: "No one is facing an immediate pay cut.
"In April, everyone will receive at least their current earnings plus any annual pay rise. Most people will get an additional pay rise on the new pay model.
"Some people are facing a reduction in pay in a year's time. Before that happens we will work together to prevent or reduce that loss.''
He said letters had been sent to most workers, informing them of their job evaluation score and its significance in terms of future pay.
Mr Moore said: "It is regrettable, to say the least, that some of the thousands of letters are wrong.
"People have been told they are having a pay cut next year when they are not, creating the wrong impression. Others have been sent a letter that refers to a previous job and therefore they, too, are not actually facing a cut or should not have had a letter at all."
He said a software fault had resulted in up to 300 people being put in the grade below the correct one. He pledged that the mistakes would be found and corrected in the next two weeks.
"Other people have been warned of a future cut when they were evaluated some years ago and their job has now changed. We can get through this with a cool head and working on facts, not rumours," said Mr Moore.
Mike Hill, a spokesman for the town hall workers' union, Unison, said: "This has caused unnecessary tension and problems among the workforce - the fact that some people have received letters indicating that they will take a drop in pay.
"We have approached the council and expressed our anger at the situation and we have received a commitment that they will put extra resources into resolving the problem. But we will stay on their backs until they sort this mess out."
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