Andrew Scheer, Leader of the Conservative Party of Canada, highlighted his concerns over proposed federal tax changes at a speech in Regina on Tuesday.
Earlier this month, Finance Minister Bill Morneau announced he was going to close tax loopholes used by private corporations.
At present, the plan would curtail "income sprinkling" or dividing income among family members. It would also end tax advantages for passive investments, like stocks and real estate, in their small businesses.
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The move has angered many groups, including farmers, doctors and small business owners. They say the changes will unfairly punish their businesses and slow economic growth.
"Now they're being told that they're cheating on their taxes, that they're avoiding paying their fair share," Scheer said in his speech. "That is an insult to every woman and man who has ever embarked on that journey to create prosperity and jobs in their community."
Morneau and Prime Minister Justin Trudeau have countered those concerns by saying the changes will make the tax system more equitable across the board.
"Tell me what's fair about that small business owner who sees their life savings taxed away," said Scheer. "Tell me what's fair about a young college student who gets told that the company that he worked for last year isn't hiring anymore."
Scheer went on to call the proposed rules the largest tax change since the 1970s, and said they were introduced in the early summer, when few people were paying attention.
"I'm very cynical about this," he said. "They brought these changes out when the House wasn't sitting, when the opposition members aren't there asking questions."
Scheer had previously called the tax plan "arrogant" and said it will kill jobs across the country.