Does anyone have any experience or know of best practice in moving monthly payment to being in arrears instead of in advance?

Employees are currently paid one month  in advance on the 1st of the month.  Obviously this can cause all sorts of recoupment problems if employees leave unexpectedly, or run out of sick pay etc during the month for which they have already been paid.

I’d like to change the system but without hitting anyone in the pocket, so it would either need to be phased in or done in the form of a loan to be recouped over time.  I’m told though, that the tax implications of either option are difficult.  I’d appreciate any suggestions or guidance.  Thanks.