Does an employer have to issue a T4A instead of a T4 for a retiring allowance?

Generally, yes. A retiring allowance is generally reported on a T4A, not a T4 — the T4 slip is used for regular employment income like salary and wages, while a payment recognized as a retiring allowance gets its own separate reporting slip. This difference matters, since it's a useful way to check how your employer has actually characterized a payment.

If you received a payment connected to the loss of your job or in recognition of long service, and it shows up on a T4 alongside your regular salary rather than on a T4A, that's worth asking about, since it may signal that the payment is being treated as ordinary employment income rather than as a retiring allowance — which affects things like whether the RRSP rollover treatment is even available for that amount.

Because how a payment is reported connects directly to how it's taxed and what special treatment might apply to it, checking which slip a termination payment actually appears on is a simple way to confirm how your employer has classified it, rather than assuming based on what it was called in conversation or an offer letter. If something looks off between how a payment was described to you and how it's actually reported, it's worth raising with your employer or a tax advisor promptly.