Toronto politician and Orange Order leader Leslie Saunders led protests against a proposal to remove the crown in 1948, a decision the government overturned.

[5] In 1956, Canada, the United States, and Mexico came to an agreement with the American Association of Motor Vehicle Administrators, the Automobile Manufacturers Association and the National Safety Council that standardized the size for licence plates for vehicles (except those for motorcycles) at 6 inches (15 cm) in height by 12 inches (30 cm) in width, with standardized mounting holes.

The new plates faced criticism from law enforcement agencies, as their new design made them difficult to read in certain lighting conditions.

Concerns were also raised that photo radar systems would have difficulty reading them, due to the lighting issues, as well as the smaller sizing of their "Ontario" text.

On February 20, 2020, Premier Doug Ford stated that the government planned to recall the initial batch, and was working with 3M on improvements.

[12] However, on May 6, 2020, a spokesperson for Ford announced that the blue plates would be discontinued entirely after "thorough testing by law enforcement and other key stakeholders".

[24] Annual fees were much lower ($18 vs $120 for a passenger car until 2022),[25] but historic vehicles may not be used as conventional transportation.

They legally may only be driven to and from events and parades where the vehicle is on display, to garages for maintenance, and other similar use cases.

Ontario vehicles registered in the International Registration Plan receive special commercial plates with "PRP" screened vertically at the left.

In the 1980s, Ontario shifted to plates that were renewed yearly with stickers, ditching the quarterly system.

They followed the quarterly system until 1980, switching in favour of a new permanent plate renewed yearly with stickers.

[28] By 1973, the quarterly system was phased out in favour of a semi-permanent plate validated each year with an annual sticker.

As of 1980, trailer plates no longer require yearly validation stickers, rather a one time fee.

Any foreign representatives and their accredited family members are required to obtain special red diplomatic licence plates when registering passenger vehicles within 30 days of taking up residence in the province.

[32] These plates are most commonly found in Ottawa and Toronto where embassies and foreign government operations are located.

Owners selecting a graphic but no custom message are generally assigned a registration with a 12XY34 pattern, where the XY is a code indicating the design (i.e.: LN and LM = Loon, CF = Canadian Flag, etc.).

The province reserves the right to refuse or withdraw plates for a variety of reasons,[37] including: While criteria have existed since the introduction of personalized plates, accusations of excessive zeal led the McGuinty government to set up a review committee in August 2008.

[40] The ownership of plates with graphic elements associated with particular groups, such as veterans or firefighters, may be restricted and require proof of eligibility.

The variety of graphics includes charities, universities, community organizations and popular Ontario sports teams, such as the Ottawa Senators.

Ontario licence plates were formerly manufactured by prison inmates at the Millbrook Correctional Centre in Cavan-Millbrook-North Monaghan.

[44] Upon Millbrook's closure in 2003,[45] manufacture was moved to the Central East Correctional Centre in Lindsay, Ontario.

[46] Since 1991, all Ontario plates have been manufactured for the MTO by Trilcor Industries, owned by the province's Ministry of the Solicitor General.

It placed an order for 100,000 units from the Waldale Irwin Holdson Group, the largest licence plate manufacturer in North America.

[53] Driving with an illegible plate is an offence punishable by fine, under the Highway Traffic Act.

[54] In 2015, the Ministry of Community Safety and Correctional Services hired Canada's National Research Council to identify the root cause of licence plate de-lamination.

[57] In the rare event that the officer chooses to issue the citation, the offence carries a minimum fine of $85.

[58] On the contrary, drivers operating a motor vehicle with defective (i.e. unreadable) number plates can be charged with the same offence.

In most cases, vehicle owners who attempted the aforementioned solutions were convicted of the same offence (HTA section 13.2).

[59] On 15 February 2020, two weeks after the province began issuing plates with the new design, off-duty Kingston Police Sergeant Steve Koopman posted a photo on Twitter showing a vehicle with the new plate at night, stating that "they're virtually unreadable at night".

[61] The redesigned plates also caused problems for photo radar cameras, which have difficulty reading the name of the jurisdiction.