Williams, who led a Progressive Conservative government in Canada's most easterly province from 2003 to 2010, launched his latest scathing attack against Harper and the Conservative Party of Canada on Sunday during an interview with CBC News.
He used the word racism in reference to the debate over the wearing of the niqab by Muslim women taking part in the oath of citizenship.
Williams said the issue is not worthy of becoming a national issue, but the Conservatives have latched onto it in order to secure votes.
"He doesn't care if he isolates the issues of women or if he isolates the issue of minorities, and even crosses, possibly, that racism line," Williams stated.
"It doesn't matter to him. It's all about getting elected at the end of the day."
Instead of voting Conservative, don't vote at all
With Canadians set to go to the polls for a federal election in just two weeks, Williams said many "progressive conservatives" have a natural inclination to vote for Harper and the Conservatives.
But he called on those who can't follow their political leanings, and are unwilling to vote for the Liberals or the New Democrats, to simply stay away from the polls on Oct. 19.
"Don't vote at all. Just don't vote for him because he's bad for the country," Williams said.
Williams's broadside is just the latest in his long-running feud with Harper, which reached its peak during the 2008 federal election when the then Newfoundland premier launched the so-called ABC Campaign (Anything But Conservative).
Williams accused Harper of breaking a promise on equalization payments, igniting an unusual rift between the two Conservative cousins.
The campaign was hugely successful, with not a single Conservative candidate winning election in Newfoundland and Labrador.
The federal Conservatives remain very unpopular in the province, which is largely a legacy of Williams's ABC campaign.
Williams left office in late 2010 with his popularity still largely intact, and his views still carry a lot of weight in the province.
Williams is obviously hoping his unfiltered attack on Harper will make a difference in a three-way race between the Conservatives, Liberals and New Democrats.
"Over time we've seen that this man cannot be trusted. He had no integrity. He's trying to stifle democracy. There's no end to what he's doing," said Williams.
"He's a lousy prime minister who's divisive."
When asked what it would take for the federal Conservatives to re-establish themselves in Newfoundland and Labrador, Williams answered simply: "A change of leadership is what's needed here."
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