Multiple sources tell The Canadian Press the package will resemble the income-splitting commitment that was a centrepiece of the Conservatives' platform in 2011, made contingent on a balanced budget.
One government insider said to expect the prime minister to roll out "a significant package that will bring relief to families and fulfil previous commitments."
The idea is that spouses would pool their incomes when they fill out their tax returns, reducing their taxable income depending on their financial situation. There is already income splitting for seniors.
The promise was wildly popular among Conservatives in 2011, but has since faced much controversy.
The late Jim Flaherty publicly raised doubts about the soundness of the policy during his final days as finance minister earlier this year.
Numerous think tanks have studied the implications of the $2.5-billion-a-year promise and found that it would benefit a relatively small number of families that are already well-off.
But others have suggested that tweaks could be made to the program's design so that it is more fair.
And many Conservative MPs believe strongly that income splitting would right a wrong that has been entrenched in Canadian tax policy for far too long.
Both the Liberals and the NDP have come out against it.
Harper and Oliver will be making their announcement at a Jewish community centre in Vaughan, Ont., and sources say it will be a big announcement with campaign-style splash.
The Conservative caucus was buzzing after Harper coyly referred to the event Wednesday morning.
Political and business circles have been waiting to see what the government would unveil in their fall economic update, which could take on the heft of a mini-budget.
Harper announced two weeks ago that the government would proceed with another campaign promise — a doubling of the child fitness tax credit.
Oliver would only confirm that the event was taking place, and he would be present. Other ministers in the Greater Toronto Area had been told to clear their schedules for Thursday.
"We're looking at a variety of policy issues," said Oliver.
"We're consulting with Canadians. We're looking at the economic data and we'll be making our decision as appropriate and communicating with Canadians."
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