Cr Michael Laws’ comments come after council biodiversity lead Alex Foulkes signalled his intention to run for the Green Party co-leadership.
In a letter addressed to councillors, Cr Laws said he was "deeply concerned that another leading staff member of the ORC is publicly aligning themselves with minority political party the Greens".
"The principle of neutrality is well understood within the public sector, including local government.
"I personally can’t trust any staff policy advice that might emanate from these two staff members given their overt championing of a political party that takes extreme environmental policy positions."
Council climate policy adviser Francisco Hernandez stood on the Green Party list and as a candidate for Dunedin in last year’s general election.
Mr Hernandez advising the councillors on climate change issues was "akin to appointing an Act party acolyte to lead the ORC on Treaty issues", Cr Laws said.
"I trust it will not elicit a code of conduct complaint but, if so, I’d be a willing combatant upon the issue of an impartial local government sector. Not just practice, but perception.
"And whether the Green Party has installed an activist cadre within the ORC staff."
Mr Hernandez and Mr Foulkes directed requests for comment to the council’s communications staff.
Council chief executive Richard Saunders said it "supported the right of individuals to participate in democratic processes".
"As a regional authority, the Otago Regional Council is politically neutral.
"We are working closely with Alex [Foulkes] to mitigate the potential conflicts of interest his nomination gives rise to, and to ensure that his political aspiration is managed outside of the primacy of his employment obligations."
The Otago Daily Times has contacted the other regional councillors for comment.
It asked whether they shared Cr Laws’ concerns, whether the public could have confidence in council staff’s neutrality, whether political affiliations of staff mattered, whether staff standing for political office risked the council’s relationship with government or reputation with the public and whether it would be appropriate for an Act New Zealand candidate to be a policy adviser for the regional council.
Mr Foulkes is one of two people who have declared their intention for the Greens co-leadership role, the other being Auckland Central MP Chloe Swarbrick.
The present co-leader, James Shaw, stands down from the position next month.
Marama Davidson is the other co-leader.