Employer asking us to repay them $6000 for collective insurance while on maternity leave

Hello everybody,

Just want to know if this is normal? My wife took 2 years off work to take care of our new daughter. When she returned to work last week she was greeted with a message that our employer kept paying for her insurance while she was gone and that now she owes them $6000 to pay them back for the insurance payments. I've never heard of this happen before so just looking for advice. Thank you

Location: Quebec