Businesses that opt to transfer employees to an affiliate during the year could be making a costly business decision. For instance, if an employee reaches their EI or CPP maximum and later transfers to an associate company, the new employer must continue paying the premium because the CRA does not observe or include the previous employer's remittances. As a result, the sum of the EI premiums and the CPP contributions made by the former employer and the successor often exceed the maximum annual contributions for the employee. And while the employee can obtain a refund for their over-payment in their tax return, business owners cannot.

https://www.pwc.com/ca/en/services/tax/sales-tax-vat-trade/canadian-sales-tax/payroll-tax/overpaying-cpp-ei-premiums.html