In Ontario's ratio'd compulsory trades, no — the sponsor has to keep a certified journeyperson on hand at a fixed ratio, and that ratio is a compliance obligation, not a suggestion.
Short answer
For trades with a set ratio, no — Ontario requires a "1:1 journeyperson-to-apprentice ratio" under the Building Opportunities in the Skilled Trades Act, 2021, with the specific trades listed in Ontario Regulation 876/21. If your certified journeyperson leaves the job or the business, the apprentice falls out of ratio immediately, and the sponsor has to fix that "as soon as possible to remain compliant" — it isn't something that can wait until the end of the day.
Skilled Trades Ontario's own guidance for sponsors states the requirement plainly: certain trades "must follow a 1:1 journeyperson-to-apprentice ratio," set under BOSTA and Ontario Regulation 876/21. That's a compliance ratio tied to the sponsor's obligations, not a workplace-safety guideline a supervisor can waive for convenience on a busy day. Worked example: a contractor running a ratio'd trade with two certified journeypersons on site can sponsor up to two apprentices at that 1:1 ratio; bringing a third apprentice onto that crew without a third journeyperson breaks the ratio the moment it happens, regardless of how experienced that third apprentice is.
Underneath the ratio question sits a separate one: in Ontario's 23 compulsory trades, you must be certified or registered to work in one to begin with. Anyone working in one "must hold a valid: Certificate of Qualification, or Provisional Certificate of Qualification, or Registered Training Agreement." An apprentice without a Registered Training Agreement isn't legally doing compulsory-trade work at all, ratio aside — the ratio question only becomes relevant once that baseline is met.
The guidance is direct about what happens when a sponsor falls out of compliance — if a certified journeyperson "leaves the business," for instance — the sponsor must "resolve the issue as soon as possible to remain compliant." That's not a passive standard; it puts the obligation on the employer to notice the gap and correct it, not to keep the apprentice working solo until someone flags it. Pair this with the glossary entry on how the ratio is counted and how site coverage gets stretched thin in the first place so a ratio breach doesn't double as an unsupervised-worksite problem at the same time.
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