Many unions and industry associations spent less on advertising in this spring's provincial election than they did in 2013, but one of the third parties who spent the most belonged to neither of those groups: Vancouver-area mayors, who spent almost $150,000 on a campaign to make the funding of major transit expansions an election issue.

The money spent by the Mayors' Council on Regional Transportation, the collection of Metro Vancouver mayors who oversee TransLink, overshadows the $130,000 spent by the province's biggest labour group and the paltry $9,700 spent by the British Columbia Real Estate Association.

Mike Buda, executive director of the Mayors' Council, said the money mostly went to producing and promoting content on social media platforms and came out of a fund for public engagement, which usually has a budget of $100,000 to $200,000 a year.

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The group also published a voters' guide a week before the election that gave the New Democrats the best grade for their commitments to the issue.

"This wasn't about influencing the outcome of the election, this was about ensuring that voters understood what was at stake," Mr. Buda said. He said the campaign was successful because all three major parties agreed to the mayors' demand that a new provinicial government fund 40 per cent of the several billion dollars' worth of new transit projects needed in the region.

The NDP promised political campaign finance reform that included banning union and corporate donations. The government says the introduction of new rules will be a priority when the legislature resumes next month.

However, changes to the rules surrounding how third parties advertise are not among the proposed reforms. Currently, third-party advertisers are required to register with Elections BC if they plan to promote their issues during a campaign. Those expenditures, limited to $166,000 provincewide, are subject to public reporting, and those reports were released Tuesday.

They show there was a slight uptick in the number of third parties that registered to advertise during the spring election, but many of the province's major unions and industry associations appear to have spent less money.

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Elections BC recorded 294 official sponsors of election campaign advertising, compared with 286 during the 2013 provincial election. While there is no official tally for how much was spent by all third-party sponsors, several backers of major ad blitzes in the previous election appear to have tightened their purse strings this April and May.

The B.C. Real Estate Association, which represents the province's 11 separate private boards for realtors, spent $9,700, less than a fifth of what it spent during the last election. The B.C. Teachers Federation spent less than half of what it did during the 2013 election – just $63,770, compared with the $138,435 it spent during a bitter battle with the incumbent Liberal Party.

The B.C. Federation of Labour, however, kept its ad spending at roughly $130,000 this election and last.

However, critics of B.C.'s lax political finance rules say the oversight of this advertising needs to be extended to the six months leading up to when the writ drops to signal the formal start of the election campaign.

The advertisers say they are educating their fellow citizens on important issues, but critics argue this "dark money" corrodes democracy in the same manner as U.S.-style super PACs – groups that operate at arm's length from politicians but function as their proxies to attack opponents and circumvent the spending limits.

Dermod Travis, executive editor of IntegrityBC, said the new government should eventually consider changes around third-party advertising outside a writ period.

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To combat dark money, he said, the government should look not at capping ad spending limits but rather at making all third-party advertisers – inside and outside the campaign period – disclose who their donors are.

"Those types of rules will go a long way," he said, noting these advertisers should meet the same criteria as political parties.