In the future I would suggest adding a clause for late payments into your contract. The longer they wait to pay you the more they make on interest. The only inc

In the future I would suggest adding a clause for late payments into your contract. The longer they wait to pay you the more they make on interest. The only incentive they have to pay you on time is to avoid being charged for it. Assuming you don't want to burn bridges I'd play it this way. Invoice them for late payment and if they call you complaining tell them that it's automated by the invoicing software you use and you'll let it slide this time. That sends them the message that prompt payment matters. If they do it a second time screw em.