The union representing Toronto's garbage collectors continued to attack attempts to privatize the service on Friday by releasing a report calling the plan "seriously flawed."

The report, released by the accounting firm Al Rosen and Associates, took umbrage with city cost estimates that claim contracting out collection for 165,000 homes west of Yonge Street would save $8 million annually.

Lawyer Al Rosen called the estimate "speculative at best," and said all the available information led him to doubt the city has gathered enough information to make an educated decision on whether to privatize the service.

"It is my opinion that city staff's costing is so fundamentally flawed that city council needs to have an independent assessment of the cost of in-house delivery," Rosen said in a statement. "How can you know whether they are saving money if they don't know how much it costs to do it themselves?"

The report was commissioned by the Toronto Civic Employees Union and Canadian Union of Public Employees Local 416 (TCEU/CUPE Local 416).

Mark Ferguson, president of TCEU/CUPE Local 416, said city council and Toronto taxpayers should have all the information before they decide whether or not to support privatization plans.

Ferguson said the city and public service workers should work together to find ways to save money and make the current system more efficient.

The union has been on the defensive since April when a city report recommended privatizing garbage from Yonge Street to Humber River, near the Etobicoke border. The report suggested cutting about 300 jobs with an estimated savings of about $8 million a year.

The union has since launched a radio campaign asking people to "stand up for public services." It also sent a series of mailouts, educating people on the potential pitfalls of privatization.

Earlier this week, a report commissioned by the Toronto Environmental Alliance suggested the cost of monitoring a private garbage collection firm would reduce the estimated savings by millions of dollars.

City council will vote on whether to privatize garbage collection next week.