Ottawa Mayor Jim Watson says he's concerned criticism levelled against the city's police chief by the head of the union representing officers could undermine public confidence in the force.

In a strongly worded letter sent to Ottawa Police Association president Matt Skof Thursday, Watson waded into the fracas and sided with police Chief Charles Bordeleau.

"I am concerned that your actions … will play a role in undermining the confidence which our residents have in all Ottawa Police Service officers," Watson wrote. The mayor added that Bordeleau continues to have "my unqualified support and confidence."

Watson's letter, sent Thursday, marks the first time the mayor has officially weighed in on the ongoing public battle between the police union and the chief — a battle that has escalated in recent months.

In March, Skof called for the resignation of Coun. Eli El-Chantiry, chair of the police services board, for failing to follow up on complaints about the police executive. The police union was also upset by the hiring of non-police staff for court security, claiming there was "misleading" information in the reports surrounding that decision.

Watson charged that Skof was being hypocritical in how he reacts to issues involving police. For example, when Abdirahman Abdi died after a violent encounter with police last month, Skof defended the officers in question.

"You asked Ottawa residents to allow the investigation to run its course, basically arguing that due process should be followed in all cases under investigation," Watson wrote.

But earlier this month, Skof told Postmedia the union was "outraged" when the Ontario Civilian Police Commission cleared Bordeleau of misconduct in his handling of a careless driving ticket issued to his father-in-law.

"You publicly bashed the OCPC because it did not deliver a finding consistent with your associations's goals," Watson wrote.

"I believe this inconsistency — calling for respect of due process in one instance and dismissing an outcome you dislike in another — will not serve your organization's interests over the long term."

The mayor's letter also alluded to a background investigator who quit over the hiring of a Somali-Canadian recruit she had deemed unsuitable for police work. The chief, who had the final say on hiring, defended the decision.

"At any given time, there will always be some who believe that they or someone else would be better suited to run the organization," Watson wrote. "Fortunately, that decision rests and will continue to rest with the Ottawa Police Services Board."

The mayor claimed he's been hearing confidentially from officers who are not pleased with Skof's representation.

"I have had several rank-and-file members of your association tell me privately that they are not satisfied with your leadership on behalf of the association and the way your have conducted yourself," wrote Watson. "That being said, you will not see me calling for your resignation as Union President because I understand and respect that it would be inappropriate for me to do so."

Watson also invited Skof to meet with him, even though the mayor has no direct authority over police operations. Neither Watson nor Skof were available for comment Friday.