The Ontario Liberal Party used a loophole in the province's campaign finance laws to amass a whopping $1.6 million during a byelection campaign in which the spending limit was $142,000, CBC News has learned.

The fundraising bonanza in Whitby-Oshawa was legal, but it illustrates how parties can use byelections to amass donations far exceeding the cost of the campaign, and how donors with deep pockets can give far more than Ontario's annual spending limits.

Data from Elections Ontario show the Liberals collected $1,632,625 during the campaign period for the byelection, which they lost to the Progressive Conservatives. In comparison, the Liberals collected $2.7 million in donations during the 2014 general election, contested in 107 ridings.

Each party's byelection candidate in Whitby-Oshawa was limited to spending about $142,700. That means Liberals have an extra $1.5 million in their coffers, to spend as they wish.

And a loophole allows them to go back to the same donors who supported them in Whitby-Oshawa for more money this year.

Byelection allows donors to exceed annual limit

The maximum donation to each political party is $9,975 per person or corporation in a calendar year. However, a donor can also give $9,975 separately for each byelection.

Fifty-one donors — mostly corporations — gave the Liberals the $9,975 maximum for the byelection campaign.

Several of those donors have already doubled down, also giving the Liberals separate, significant donations for this calendar year. CN Rail has given another $8,000, the Canadian Generic Pharmaceutical Association another $6,000, and Colleges Ontario — which represents the province's publicly-funded colleges — has given the Liberals $6,000.

This revelation comes amid a furor over political fundraising in Ontario and promises of reform.

The Progressive Conservatives raised $783,809 during the byelection campaign — less than half the Liberal total. Five donors donated the maximum $9,975 to the PCs.

The NDP raised a mere $51,319, with no donor giving more than $1,330, the limit for a donation to a constituency association.

Donors who gave maximum $9,975 to Ontario Liberal Party in Whitby-Oshawa byelection