Ontario's Progressive Conservatives are calling on NDP Leader Andrea Horwath to part ways with a candidate in Toronto who shared an Adolf Hitler meme on social media several years ago.

At a morning news conference, two PC candidates, Todd Smith and Gila Martow, presented what they say is evidence of anti-Semitism "festering" in the NDP.

The pair provided a printout of an October 2013 social media meme shared by the NDP candidate in Scarborough–Agincourt, Tasleem Riaz.

The Facebook post features a quote that is commonly attributed to Hitler overlaid over a photo of the tyrannical despot giving a Nazi salute to a gathered crowd. A title above the image reads, "The Ruler said about Rule."

The phrase below it — "If you don't like a rule ... just follow it ... reach on the top ... and change the rule," is attributed to Hitler, though there's no direct historical evidence the Nazi dictator ever uttered it.

Smith called the post the "most serious example of anti-Semitism we've seen in Ontario politics for a long, long time" and criticized Horwath for what he characterized as a laissez faire approach to dealing with candidates who express controversial views.

"You don't post this kind of thing by accident. You don't openly push Nazi messages on social media by mistake," Martow said.

Smith and Martow also provided a screen grab of a April 2011 post allegedly written by Riaz, taking aim at the federal Liberals' and Tories' support for the war in Afghanistan. Riaz said the parties supported troops who "slaughter innocent men, women and children."

In a statement, Riaz said she is "horrified that an inappropriate meme was on my Facebook page" and that she cannot understand how it happened.

"I don't recall sharing it in 2013 — and at no point in my life would I have done so intentionally," she continued.

"I am an interfaith advocate, and I have devoted my life to interfaith religious tolerance and freedom. I work closely with the Jewish, Hindu, Christian, Sikh and Muslim communities in my neighbourhood. In every way, I find Hitler, the hate he spewed, and the genocide he committed to be abhorrent."

PCs in 'glass house,' Horwath says

During a campaign stop on Friday morning, Horwath said she was unaware of the details of the post and would have her staff investigate the allegations. She followed up, however, with a statement of support for Riaz.

"Let me be pretty clear about our candidate. I've known Tasleem for some time now. This woman is an activist in the inter-faith community … I find it pretty unbelievable that she would be in any way implicated in anything that's at all anti-Semitic," Horwath told reporters.

She added that PC Leader Doug Ford and his team "live in a little bit of a glass house."

"This is coming from a party whose leader is accused of cheating in nomination meetings, cheating in the democratic process," Horwath said, alluding to allegations that Ford improperly bought party memberships to support his preferred candidate in Etobicoke Centre.

Shortly after Horwath spoke, Liberal Leader Kathleen Wynne said on Twitter, "Andrea Horwath needs to be clearer in her condemnation of this post by her candidate.

"No one in Ontario can or should attempt to draw inspiration from the words of Adolf Hitler. Canadian soldiers have earned and deserve our thanks."

The social media footprints of NDP candidates have come under increasing scrutiny from the PCs on the campaign trail in recent weeks. Earlier this week, Horwath was forced to fend off criticism of the NDP candidate in Mississauga Centre, Laura Kaminker, who once posted online that she refuses to wear a poppy around Remembrance Day.

The PCs are not immune to ghosts of social media past, however.

Andrew Lawton, the Tory candidate in London West, faced pressure to resign after a series of posts — alternately described by critics as homophobic, misogynistic and Islamophobic — resurfaced online. Lawton has repeatedly attributed the posts to mental illness.

Despite calls for him to intervene, Ford has allowed Lawton to continue on the campaign trail.

Pressed by reporters to explain the apparent contradiction, Smith said the difference is how the PCs have chosen to handle controversial comments from candidates.

"Our candidates have apologized and addressed comments that were made. The NDP continue to shrug them off, and their leader, Andrea Horwath, continues to almost laugh off these types of comments that were made in the past," said Smith.

"True leadership is actually addressing these situations as real problems and answering the questions that need to be asked about this party."