Stephen Harper's Conservative Party is fighting changes to federal ridings in Saskatchewan after an independent commission recommended new boundaries that should make it easier for Tom Mulcair's NDP to regain a foothold there.

Tory MPs are expected to file objections to a parliamentary committee in an effort to require the Saskatchewan boundary commission to reconsider its proposal to create five entirely urban ridings in the province – two in Regina and three in Saskatoon.

Today, federal ridings representing Regina and Saskatoon voters are pie-shaped combinations of urban and rural electors that each include a piece of the city and then run deep into the adjoining countryside. The Conservatives, who have proven adept at winning rural support, have managed over the years to capture all but one seat.

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Other parties, including the NDP, are also challenging proposed riding boundary changes in some provinces.

But the Conservatives acknowledged this week that they went one step further, paying for automated phone calls – robo-calls – that criticize the Federal Electoral Boundaries Commission's work and appear to be designed to drum up opposition to the changes in Saskatchewan. The calls last week went to thousands of households across the province.

The script of the robo-call message, a sample of which was obtained by The Globe and Mail, confirms reports that it was a "push poll," a negative marketing campaign disguised as polling research.

"The Saskatchewan boundary commission has decided to ignore our important traditions and history," the automated message warned Saskatchewan listeners last week.

"They are destroying our federal ridings and pitting urban against rural interests by creating federal ridings that would elect urban-only members of Parliament."

It asked listeners to press "two" on their phone if they favour keeping ridings "as they are" or "three" if they favour a "drastically altered" map that creates urban-only ridings.

A Tory party spokesman this week described the calls as an effort to "communicate with voters and get their feedback."

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The party wasn't identified as the source of the calls– an omission Conservative Saskatchewan MP Tom Lukiwski later acknowledged was deceptive.

The NDP accused the Conservatives of trying to put pressure on the boundaries commission. The New Democrats won about a third of the popular vote in Saskatchewan during the 2011 ballot but failed to win a seat.

Saskatchewan is the birthplace of the political movement that went on to become the NDP, but the party lost its remaining two seats there in the 2004 federal election.

The Conservatives, who now control 13 of the province's 14 federal seats, have gone to great lengths to keep their Saskatchewan stronghold intact.

The Harper government rejected a 2010 foreign takeover of Saskatchewan's iconic Potash Corp. after a public backlash that had MPs worried they'd lose close to half their seats if they approved the deal.

The Prime Minister insisted on Wednesday the Tory push poll broke no rules and he described opposition to the changes as "overwhelming" in the Prairie province. "We are simply operating within the process," he said.

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Mr. Harper said the Tories will leave the final decision to the boundaries commission.

"Some years ago, the Liberals tried to bring in partisan legislation to overturn boundary commission recommendations. We would never do that," he told the Commons.

The Conservatives argue they're trying to preserve a system that balances urban and rural interests and note the NDP had previously managed to win seats under existing boundaries. The Tories also point out that one of the members of the boundary commission, David Marit, issued a dissenting report opposing the changes. Mr. Marit also said in his minority report that close to 75 per cent of the letters and public submissions the commission received were against the changes.

NDP democratic reform critic Craig Scott said the Tories tripped up when they resorted to robo-calls.

"NDP MPs are following the rules and will continue to take part in the democratic process, namely, submissions to the Procedure and House Affairs Committee. Unlike the Conservative Party, NDP MPs would never countenance a deceitful phone campaign designed to coerce an independent boundary commission to bow to political pressure," Mr. Scott said.

Mr. Justice Ron Mills, the chair of the Saskatchewan commission, described public opinion on the changes as mixed.

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He made a point of noting that number of submissions received had the "sole intention" of promoting a particular political candidate, either elected or defeated. He said under the law "that type of submission was irrelevant."

Justice Mills said if he was asked to reconsider his recommendations, he would only base the rethink on what MPs argue in their submissions -- and not on any other commentary such as the push poll.

The Conservatives say the NDP is unfairly demonizing robo-calls even though the New Democrats also use automated dialers for political ends. They pointed out the NDP employed robo-calls in January, 2012, to attack defecting MP Lise St-Denis after she quit the NDP for the Liberals. The New Democrats hired a company to call households in her riding with a message criticizing the defection and offering to transfer listeners to her riding office so they could express their disapproval.