TORONTO -- The man about to become Ontario's top cop should step aside while a probe is conducted into allegations of political interference from Premier Doug Ford's office in his hiring, the leader of the Opposition said Wednesday as the government stood firm on the appointment.

NDP Leader Andrea Horwath called on Toronto police Supt. Ron Taverner -- a Ford family friend who was named Ontario Provincial Police commissioner last month -- to "do the right thing" a day after the force's acting chief joined a growing chorus in questioning the Progressive Conservative government's choice for the job.

Acting OPP Commissioner Brad Blair sent a letter to ombudsman Paul Dube on Tuesday night asking him to probe Taverner's hiring, saying officers in the force expressed concerns the selection process was unfair and could raise doubts about the police service's independence.

Blair also suggested in the letter that Taverner's appointment be delayed until an investigation could be conducted by the ombudsman -- a proposal Horwath supported in comments she directed at Taverner.

"You know that this requires your action since Mr. Ford and the government ... are not prepared to act," Horwath said. "You have to step aside for the sake of the organization of policing that you've dedicated your whole career to. This is the time you have to show your integrity."

Taverner, a longtime Ford ally who initially did not meet the requirements listed for the commissioner position, did not immediately respond to request for comment. The 72-year-old is set to take on his new role on Monday.

Community Safety and Correctional Services Minister Sylvia Jones defended both his appointment as commissioner and the process that led to it. She said the government fully disputed the contents of Blair's letter.

"We are not going to comment on Mr. Blair's motivations for using the office he holds to raise these issues," she said. "The government stands by the process leading to the appointment of Mr. Taverner."

Jones also said the government would respect any decision the ombudsman makes around opening an investigation and would co-operate if a review gets underway.

Meanwhile, Horwath also called on the RCMP to investigate allegations in Blair's letter that Ford's chief of staff, Dean French, asked the OPP to purchase a "larger camper type vehicle" and have it modified to the specifications of the premier's office.

Blair alleged the chief of staff then provided specifications to an unnamed OPP staff sergeant and asked that the costs associated with the vehicle be "kept off the books."

The allegations appear to violate the province's financial rules, Horwath said.

"We also have to deal with the nonsense around the pimped out ride that Mr. Ford has requested from the OPP. And (allegedly) hiding it from the books," she said. "This is not what people wanted ... They did not ask for this kind of behaviour from the new government."

Days after naming Taverner as the new commissioner in late November, the Ford government admitted it lowered the requirements for the position to attract a wider range of candidates for the job.

Blair's letter said the original commissioner job posting required candidates to have a rank of deputy police chief or higher, or assistant commissioner or higher, in a major police service -- a threshold Taverner did not meet.

Of the 27 candidates, Blair, who was an applicant himself, contended only four did not meet the original threshold requirements.

He said Taverner's hiring process "remains enveloped in questions of political interference" and should be addressed by impartial review.

Liberal legislator Marie-France Lalonde said the allegations in Blair's letter are shocking and Taverner should step aside while an investigation is conducted. She lauded Blair for coming forward, despite the risk to himself and his career.

The premier did not address the allegations swirling around Taverner's hiring Wednesday, making no mention of the controversy during a brief speech at the International Economic Forum of the Americas in Toronto. Ford also did not stop to speak with reporters gathered at the event.

Last week, the government maintained Taverner was appointed according to his own merits, a claim Jones reiterated Wednesday while stressing his five decades of service with Toronto police.

Ford has also repeatedly stressed his long relationship with Taverner was not a factor in the decision.

University of Toronto law professor Kent Roach said the controversy shows there is a need for stronger firewalls between the police and the premier's office. He said the Taverner situation also raises broader concerns about public trust in the police that the Tory government will now be forced to confront.

"I don't think this is going to go away," he said. "Even if it somehow did ... with respect to the appointment, I would still think there are some lingering and troubling questions about police/government relations going forward."

-- with files from Michelle McQuigge.