"People should be appalled that the premier has put the office of the premier in this situation," said interim Progressive Conservative Leader Jim Wilson.
"It's unseemly at the very least and it's very, very worrisome to see that once again we have Liberals on the carpet for possible criminal activity," said NDP Leader Andrea Horwath.
The Ontario Provincial Police are investigating allegations the Liberals offered a job or appointment to Andrew Olivier, their Sudbury candidate in 2014, to step aside in favour of Wynne's preferred choice for the byelection, then-NDP MP Glenn Thibeault.
Wynne has always maintained there was no need to offer Olivier anything because she'd already decided he wouldn't be the Liberal candidate, but she wanted to keep him active and involved in the party.
It will be up to voters to decide if they want to pass judgment on the fact the premier is being questioned by police, said Wynne.
"It's up to the public to make that determination," she said. "I've said I will work with the authorities."
Wynne promised to co-operate fully with the police probe.
"If there's a question that's being asked and I have to answer it, then I will sit with the person who's asking the question and answer the question," she told reporters.
The Tories also criticized Wynne for postponing her interview with the OPP for weeks because of apparent scheduling conflicts.
"No other citizen in the province would be allowed to avoid being questioned for as long as she has," said Wilson. "She must consider herself above the law, and it certainly looks that way to the average Ontarian."
Just before the byelection, Olivier said he was offered an appointment to step aside as the Liberal candidate in conversations with Wynne's deputy chief of staff, Pat Sorbara, and with Sudbury Liberal Gerry Lougheed, who chairs the city's police services board.
"You don't go do those things without permission of the boss, and Premier Wynne's the boss," said Wilson.
Both Sorbara and Lougheed have denied the allegations and Wynne has refused repeated opposition calls to remove Sorbara from the premier's office until police complete their investigation.
Olivier made public audio recordings of his talks with Sorbara and Lougheed, prompting police to reopen an investigation they had previously deemed closed. Wynne's conversation with Olivier was not recorded.
The OPP began investigating allegations the Liberals' actions violated the Criminal Code, and later began looking into possible violations of the Election Act as well.
Elections Ontario concluded Sorbara and Lougheed's actions constitute an "apparent contravention'' of the Election Act concerning bribery, but the agency has no mandate to conduct prosecutions.
After quitting the federal NDP and resigning his seat in Parliament, Thibeault recaptured Sudbury for the provincial Liberals, who lost the riding to the NDP in the 2014 general election.
The Liberal government also faces police investigations into financial irregularities at the Ornge air ambulance service and into the deletion of government documents on cancelled gas plants in Oakville and Mississauga.
Follow @CPnewsboy on Twitter
Also on HuffPost