However, through Facebook he sent a message to the human resources manager asking for her address in order to serve documents, because he was making a discrimination claim.

Catanzariti, who is the President of the NSW Law Society, wrote to Mitchell informing him that his online activities and tone of message were "cause for concern", reported The Sydney Morning Herald.

"It is reasonable to draw an inference that you have engaged in similar searches for other Clayton Utz staff with whom you are apparently aggrieved," he wrote.

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"Clayton Utz ... will not countenance any stalking, harassment or intimidation of its staff ... Affected individuals may want to take independent legal and other steps to protect themselves."

Mitchell, who has failed in attempts to bring harassment, discrimination and victimisation claims against former colleagues, including Catanzariti, denied he had done anything illegal and said the threats constituted bullying.

He is pursuing his claims by appeal in the Administrative Appeals Tribunal. Catanzariti declined to comment on the case while it was still in litigation.