Does buying the business reset an employee's eligibility for a pension they were vesting into?

It depends heavily on your deal structure and on the specific pension plan's own terms, which govern vesting more directly than any general rule about business sales. In a share purchase, the plan and its administration generally continue unchanged along with the corporation, so an employee working toward vesting continues under the same plan on the same terms as before, with no reset.

In an asset purchase, the outcome depends on what happens to the pension plan itself: if you're continuing the same plan (less common, but possible in some structures) or a comparable plan is put in place with credit given for prior service, vesting progress may carry forward; if the employee is moving to an entirely new plan with no service-bridging provision, their vesting clock may effectively restart under the new plan's own rules, since a new plan generally applies its own eligibility terms rather than inheriting time accrued elsewhere.

This is a plan-specific and often actuarial question as much as a legal one, so review the actual plan documents and get pension-specific advice rather than assuming either outcome. A Treadstone business lawyer can help coordinate this alongside your broader employee transition planning.