David Russell, director of human resources at the LSC, was "aggressive, threatening and intimidating" towards the union official, behaviour not expected of an employer, claimed Mark Serwotka, general secretary of PCS, which represents people working in or for government agencies.
Mr Russell told the union he was "amazed and incensed to learn that your officials have been briefing the press against the LSC...".
Regional union official Johanna Baxter had told FE Focus that people at the Nottinghamshire council "are so frightened they will not put their heads above the parapet". A "culture of fear" existed at the council, with people afraid of being slapped down if they spoke out, according to a consultants'
report leaked to FE Focus.
When Mr Russell read Ms Baxter's comments he asked to see her and, the union claims, tried to bully her.
Talks between the union and the council over pay and redundancies are at a critical stage. In his letter Mr Russell implied the union's negotiating status might be threatened as a result of Ms Baxter's remarks.
He asked whether the union approved of the official's actions. "These comments were a serious error of judgement and call into question the value of the partnership agreement and the jointly agreed procedures we have with you for resolving grievances."
Mr Serwotka said Ms Baxter had honestly reflected the feelings of a number of the union's members at the council. The union had the right to express independent views to the media when asked to do so.
Ms Baxter "had raised concerns with the national LSC about the management style in Nottingham and of members' fears of raising individual grievances".
"Unfortunately the national office was not prepared to take this up and it is not surprising therefore that someone has felt the need to give information to the press."
Rob Valentine, executive director of the Nottinghamshire council, has told staff he knows of no grievances raised either locally or nationally. But staff claim numerous complaints have been made to him.
Mr Valentine told staff he was "disgusted" with what the union official had told FE Focus, and he hoped that David Russell, and John Harwood, LSC chief executive, would raise it with PCS at the highest level.
In a statement, Mr Russell said: "We have built a very constructive relationship with the PCS ... and we are not prepared to conduct our employee relations through the press.
"LSC staff are entitled to work in a place which is free from bullying and harassment. There are jointly-agreed grievance procedures in place between the union and the LSC. We must use these to protect our staff and their rights. This is an internal matter for the LSC" The LSC and union will meet on August 4 to discuss Nottingham.