TORONTO -- As Ontario’s Liberals elected their new leader on Saturday, a massive labour rally took the spotlight outside, where thousands gathered to send a message to the future premier.

Unions representing teachers, public service employees and others lined the police barricades outside the former Maple Leaf Gardens, chanting “Down with Liberals.”

Many of them booed Liberal delegates and other attendees as they entered and exited the building on Carlton Street.

Toronto police estimated that 15,000 protesters flooded the streets at one point, marching down Gerrard, Yonge and Carlton streets. The Ontario Federation of Labour had said that 25,000 people from across the province were expected to attend.

Demonstrators arrived by the busload to the downtown core. Dozens of buses, bearing pick-up location signs like “Kitchener-Waterloo,” “Hamilton” and “London area,” lined Jarvis Street and nearby roads as the OFL kicked off the protest with a rally at Allen Gardens.

OFL president Sid Ryan urged the crowd to send a strong message to Liberal leadership candidates by flooding their social media streams with messages about collective bargaining and labour rights.

Unions say the Liberal government’s policies and austerity measures have destroyed well-paying jobs, benefits and employment security.

Many of those in the crowd were teachers, angry about Bill 115, the recently repealed piece of legislation that imposed contracts on teachers who did not negotiate agreements with the province.

Education Minister Laurel Broten said the government had to act to protect students from teachers’ strikes, but later acknowledged that Bill 115 had become a “lighting rod.”

Teachers’ unions, however, said that repealing the bill was a “meaningless” move that didn’t address the rift between them and Queen’s Park.

“We just want our right to fair collective bargaining,” said Doug Reeves, a teacher who arrived from London, Ont., to take part in Saturday’s protest.

Reeves, who has been teaching for 24 years, said he was pleased to see a boisterous, “aggressive” crowd outside the Liberal leadership convention.

“They can’t ignore us now,” he said.

After Kathleen Wynne's victory was declared Saturday night, the Elementary Teachers’ Federation of Ontario issued a statement saying it hopes that "respectful discussions can begin to help end the chaos in schools created by Bill 115."

“We hope that Premier Wynne will govern in the best interests of working people in Ontario and restore the democratic values that have shaped this province,” ETFO President Sam Hammond said in a news release.