Sean Kelly, 34, was elected to serve as one of three Unison officers in April last year – but just weeks later, he was suspended by Sunderland Council over claims he had bullied and harassed other officials.
Mr Kelly, of Grafton Road, Whitley Bay, was later allowed to return to work by council bosses.
But he has launched a legal claim against council chiefs who he says blocked his right to serve his union members.
Through his representative Yunus Bakhsh, Mr Kelly, who worked for Sunderland social services before becoming a union official, made a series of claims against the council at an employment tribunal in Newcastle. The council denies trying to hinder his work.
John Rawling, the council's assistant head of corporate personnel, outlined a chain of events that had begun in February last year when Unison branch secretaries Jackie Gallagher and Tina Roche lodged a formal complaint of harassment against Mr Kelly's predecessor, Bob Scott.
As the Scott investigation began, the tribunal heard allegations were raised against Mr Kelly and his "intimidating manner".
Mr Rawling said Mr Kelly had declined to be interviewed as part of the investigation and begun talking about getting "a vote of no confidence" for the other two branch secretaries .
Matters then came to a head in May when Mr Rawling saw a letter from Mr Kelly which was addressed to union members.
Mr Rawling said the letter stated there was a "flawed" investigation and an "attack" was being made on Mr Kelly.
"I saw this as absolute confirmation that he was refusing to co-operate with the investigation. I was very concerned about Sean Kelly's outrageous behaviour."
Council bosses decided he should be suspended and there were no objections from Unison bosses.
Mr Kelly claimed in another letter that the council was trying to de-recognise the union, which was not true, added Mr Rawling.
The tribunal is expected to finish on Friday.