Two payroll systems and one pay run

The situation

A platform company executing a buy-and-build strategy acquired a smaller regional competitor in an asset purchase and moved immediately to integrate the target's roughly 60 employees onto its own payroll and benefits platform, aiming to have everyone paid on the acquirer's system by the next scheduled pay date — nine days after closing.

The integration playbook, built for a prior acquisition in a different province, treated the move as onboarding: each employee entered into the new HRIS as a new hire, with a start date equal to the date of acquisition.

The problem

Ontario law does not treat an asset-sale employee transfer as a fresh start. The Employment Standards Act, 2000 deems length of service to flow through from seller to buyer: the guide to the Act confirms that “a person's length of employment with the seller of a business…is attributed, or ‘flows through’ to the purchaser of the business,” and that “the new employer has to recognize the time the person worked for the previous employer.” Treadstonelaw's own summary of the same continuity rule confirms the mechanism directly: “section 9 of the Employment Standards Act, 2000 deems employment continuous where the buyer hires the seller's employees, so service dates flow through into notice, severance and vacation entitlements”.

The exception is narrow and did not apply here, though it is often described with a condition that is not in it. It turns on the length of one gap and nothing else. A person’s employment with the previous employer is not attributed to the new owner where the employee “is hired by the new owner more than 13 weeks after the employee's last day of employment with the seller or the day of the sale, whichever is earlier.” It does not matter who ended the earlier employment, and it does not matter whether the buyer declined to rehire and then changed its mind. The Ministry’s own worked examples run in both directions to make exactly that point: an employee whose employment the seller ended ten weeks before the sale and who was rehired eight weeks later loses continuity, and so does an employee the buyer declined to hire and then recalled sixteen weeks after the sale. Every employee here was retained without a gap, so every one of them kept their original service date whether the new HRIS recorded it or not.

What it cost

Because the migration had reset service dates to the closing date, the first vacation-accrual run under the new system calculated entitlements as if every employee had started that week. For a handful of employees with five, eight and even fourteen years of continuous service at the target, that meant a visible, immediate cut in accrued vacation entitlement on their very first pay stub from the new owner — the single fastest way to turn a quiet integration into a wave of complaints and, on Ontario law, a live entitlement the ESA does not let an employer simply reset by relabelling a hire date.

Treadstonelaw's guidance flags the second-order risk in the same breath: “Changing terms unilaterally after closing risks constructive dismissal, and harmonising two benefit plans is the most common way that happens by accident.” That is a live exposure for a buyer that had, without intending to, treated 60 continuing employees as new hires.

The fix

HR and payroll rebuilt the migration file before the second pay run, importing each employee's original hire date with the seller (not the closing date) as the service-date field driving vacation accrual, notice entitlement and any tenure-based benefit. The correction was retroactive to the first pay period, and the company issued a short written notice to affected employees explaining the correction rather than letting it surface as a silent fix.

For the next acquisition, the integration checklist added a mandatory field mapping step before any payroll cutover: service date, not hire date into the new system, is the number that governs — confirmed against employment records before the first combined pay run, not corrected after it.

The wider lesson

The ESA's continuity rule is worth stating plainly because a buyer's own systems vendor rarely warns about it: a payroll or HRIS platform will happily let an administrator enter any hire date at all, and nothing in the software stops a team from entering the acquisition date by default. The guide to the Act is explicit that the obligation runs the other way — “the new employer has to recognize the time the person worked for the previous employer” — and that obligation exists whether or not the new system's onboarding wizard was ever built with an asset-deal continuity field in mind. Treat the systems migration and the employment-law review as two separate workstreams reporting to the same integration lead, not one IT project with a legal sign-off at the end.

Takeaways

• • On an Ontario asset deal, ESA s.9 deems employment continuous when the buyer hires the seller's employees — service dates carry forward into notice, severance and vacation, regardless of what a new HRIS record says.
• • Continuity breaks only where the employee is hired more than 13 weeks after the earlier of their last day with the seller and the day of the sale — regardless of which side ended the earlier employment. A same-week integration does not create that gap.
• • A payroll or HRIS migration is not just a systems project after an acquisition — it is an employment-standards compliance exercise, and the service-date field is the one that matters most.
• • Fix a service-date error retroactively and in writing the moment it is found; a silent correction invites the same distrust the original error caused.

Sources

• • Ontario, Your guide to the Employment Standards Act — Continuity of employment — the government guide, not statutory text (ontario.ca/laws serves a JavaScript shell and cannot be fetched). Source of “attributed, or ‘flows through’ to the purchaser of the business,” of “the new employer has to recognize the time the person worked for the previous employer,” and of the 13-week gap exception and its two worked examples.
• • Treadstone Law — post-closing integration — source of both quoted sentences: the section-9 continuity rule and the constructive-dismissal risk from unilateral post-closing term changes. This is where the s.9 section number in this file comes from; the statutory text itself could not be fetched.
• • Treadstone Law — does continuity of service reset in an asset purchase? — independently states the same rule and the same limit: prior service “counts as service with you for entitlements like vacation, leaves, and notice or severance,” and continuity “generally doesn't apply if you hire the employee more than thirteen weeks after the earlier of their last day working for the seller or the date of the sale.”