Anyone working one of Ontario's 23 compulsory trades — and 'anyone' includes journeypersons, who still have to renew it every year.
Short answer
Anyone performing work in one of Ontario's 23 compulsory trades — plumbers, electricians, steamfitters and hairstylists among them — must hold a valid Certificate of Qualification, Provisional Certificate of Qualification, or Registered Training Agreement. Everyone in a compulsory trade sits a certifying exam, and journeypersons must renew their certificate every year, not just earn it once.
Skilled Trades Ontario's own list is specific: “In Ontario, there are 23 compulsory trades. Some examples include plumber, electrician, steamfitter and hairstylist.” The credential requirement is just as specific — “to work in one of the 23 compulsory trades in Ontario, you must hold a valid: Certificate of Qualification, or Provisional Certificate of Qualification, or Registered Training Agreement.” And it isn't a one-time hurdle: “all compulsory trades have certifying exams. Journeypersons in compulsory trades must renew their Certificate of Qualification each year.” (See Skilled Trades Ontario's guide to compulsory trades.) A worker who earned the certificate five years ago but let the annual renewal lapse is not, at that moment, legally qualified to perform the work.
There are named exemptions, and they're narrower than most people assume. OYAP participants and ministry-approved pre-apprenticeship trainees are exempt while in the program. Permanent employees of an industrial plant get an exemption too, but it explicitly does “NOT extend to maintenance and repair work on vehicles registered for use on a highway under the Highway Traffic Act” — the industrial-plant carve-out doesn't follow the worker off-site or onto road-registered equipment.
Quebec reciprocity is real but limited to seven named trades: Electrician – Construction and Maintenance; Hoisting Engineer – Mobile Crane Operator 1; Plumber; Refrigeration and Air Conditioning Systems Mechanic; Sheet Metal Worker; Sprinkler and Fire Protection Installer; and Steamfitter. Holders of the equivalent Québec certificate, or registered Québec apprentices, in one of those seven can rely on that credential — but outside that specific list, a Québec certificate doesn't substitute for Ontario's own.
The compulsory-trades framework is a different question from whether a credential earned in another province transfers into Ontario at all — see whether a Red Seal works across provinces — and it comes up constantly during a business sale, where every apprentice tracking toward one of these certificates needs the sponsorship question resolved before closing: what happens to apprentices on a sale.
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