A New Jersey man who founded a wastewater-treatment company is still acting like a boss — even though he was fired in December, a lawsuit claims.

Mark Fosshage had served as World Water Works’ CEO since 2012, but in November the company decided not to renew his employment deal — a move Fosshage “acknowledged and accepted,” the company claims in a Manhattan Supreme Court lawsuit.

But Fosshage, 45, quickly changed his tune, showing up uninvited for meetings at the Oklahoma-based company’s offices; meeting with a key vendor as if he was still CEO; emerging as the “driving force” behind a shareholder lawsuit against World Water Works; and suing the company twice.

“Fosshage refuses to accept the termination and continues to wrongfully and without right insinuate himself into, and thereby interfere in, the company’s affairs,” World Water Works charges in court papers.

Fosshage’s lawyer denied the accusations, saying the one-time CEO is fighting to prevent the company’s possible relocation to India. “He has 86 employees in the US, and he wants to keep them here,” Gilberto Garcia said.