Ontario's municipalities say they're hoping the province will make good on its pledge to ensure the proposed minimum wage law won't send them into the red.

Premier Kathleen Wynne got an earful about the proposed legislation from elected officials at the annual meeting of the Association of Municipalities of Ontario in Ottawa this week.

Bill 148 would boost the minimum wage from $11.40 to $15 per hour, starting in 2019.

It would also bring in equal pay for part-time workers and increase on-call pay for firefighters and other emergency workers.

Municipal workforces in Ontario are heavily unionized, and some municipalities are worried the unions will agitate for salary increases for their members if the minimum wage rises.

As well, smaller municipalities rely heavily on part-time and on-call workers, so the provisions in Bill 148 are expected to hit them especially hard.

Smiths Falls Mayor Shawn Panko said salaries make up 75 per cent of the town's budget, and worries the provisions in the bill will cost his community thousands, and force property taxes up.

"I hope that we see some changes to the bill before it passes in the house," Panko said.

"It would absolutely bankrupt a lot of our communities," said Kenora Mayor Dave Canfield to applause from other attendees at the town hall-style discussion with the premier at Ottawa's Shaw Centre on Tuesday.

"Would you please commit to either completely trashing bill 148 altogether, or at least sit down and come up with something reasonable that's not going to bankrupt us?" he asked Wynne.

"We're not going to trash Bill 148," Wynne replied, but she promised to work with municipalities to make sure there are "no unintended consequences" of the legislation.

A study commissioned by the Ontario Chamber of Commerce estimates municipalities will be forced to increase employee wages by $500 million if the bill passes unchanged, and if they're unable to find offsetting revenues.

Large municipalities appear less affected by the proposed changes. Ottawa Mayor Jim Watson said the provisions in the bill would likely mean $2 million in extra spending, or less than 0.1 per cent of the city's $3-billion annual budget.