The backlash against Canada Post is growing, with four mayors in the greater Montreal area joining the legal battle against the Crown corporation's decision to phase out urban home mail delivery by 2018.

Montreal Mayor Denis Coderre says he and the mayors of Laval, Longueil and Westmount are frustrated with the "cavalier" approach of Canada Post to complaints about community mailboxes since the plan was announced in December 2013.

They'll be joining a union lawsuit before the Federal Court aimed at overturning the post office's decision to replace door-to-door delivery with so-called "superboxes."

Here are some of the efforts underway to fight Canada Post.

Canadian Union Postal Workers

CUPW represents 54,000 postal workers across the country. The union wants the Federal Court to declare the cancellation of home mail delivery as unconstitutional, a violation of the Charter of Rights and Freedoms.

The union says the shift to community boxes for mail delivery will eliminate up to 8,000 jobs.

Montreal mayors

Coderre says he and other mayors will first be asking the court to make sure they can be a "full participant" in the lawsuit.

"We want to send a strong message that everybody's in it, and that there are real issues." He says the next step is to win a moratorium on the installation of the curbside mailboxes.

The mayors say some boxes end up on private property with no public consultation. They say others are in unsafe locations, or are difficult for seniors to reach, while some may impede the flow of traffic.

Londoners for Door to Door

A campaign in London, Ont., where the post office has already implemented community mailboxes, is conducting door-to-door canvassing against the policy.

Organizers of Londoners for Door to Door have been lobbying city council to set up a public consultation process, something demanded in the City of Montreal's report released last February detailing the effect of Canada Post phasing out door-to-door delivery.

Hamilton levies charge for group mailboxes

The City of Hamilton is due in Ontario Superior Court the week of May 25 to answer a challenge filed by Canada Post, which is fighting a bylaw passed in April aimed at restricting the installation of community mailboxes.

Community mailbox

Community mailboxes have been redesigned, but opposition remains to their adoption. (Canada Post)

Under the bylaw, the Crown corporation must pay $200 per superbox and consult with the city on the placement. Bylaw officers can lay provincial charges if Canada Post ignores the new rules and have already issued eight fines to Canada Post.

Four Hamilton city councillors recently wrote to the federal government, alleging the corporation cut through a gas line while installing a mailbox.

Canada Post argues the bylaw conflicts with the Canada Post Corporation Act.

But City of Hamilton solicitor Janice Atwood-Petkovski says the city does have authority over road allowances and rights of way.

She says recent case law shows the city can put its foot down when it's worried about resident safety.

York Region

Canada Post started introducing the group mailboxes in the suburbs, in places like York Region, north of Toronto.

A town councillor in Aurora, Tom Mrakas, tabled a motion this month to change bylaws to follow Hamilton's lead and charge Canada Post a fee for each mailbox it installs.

Mrakas has been quoted as saying there should be a "meaningful conversation" with residents regarding the placement of the boxes.

B.C.'s long-standing complaints

Documented warnings about community mailboxes by British Columbia municipalities made headlines several months before news broke that door-to-door mail delivery would end across the country.

'Canada Post reduced services and increased stamp prices even before email was invented.' — Peter Trent, mayor of Westmount

More than 130 communities filed 4,800 complaints to the Crown corporation between 2008 and 2013, according to documents obtained by CBC News.

There were several reports of break-ins, raising fears about lost or stolen mail and identity theft.

About a third of Canadian households, 5.1 million of them, were getting door-to-door home delivery before the phase-out plan began to be implemented.

The post office says that in 2012 its carriers delivered one billion fewer pieces of mail to Canadians than in 2006.

In announcing the new system, Canada Post pointed to a Conference Board of Canada report released in April 2013. It concluded the corporation would face a loss of $1 billion a year by 2020 if it chose to remain with conventional mail delivery.

Westmount Mayor Peter Trent on Friday said it's simply not true that the current mail system has outlived its usefulness.

"Canada Post reduced services and increased stamp prices even before email was invented," Trent told reporters in Montreal. "I'm a little tired of hearing that we have to get with the program and that social media has made mail service extinct."