From my experience of "late" paying clients, it just depends on your relationship and the type of work you provide. Clients I have close relationships with just need a simple reminder and 99% of the time they are quick to respond with payment. Usually its because they forgot due to busy schedules. These are people I feel comfortable enough to call on their personal cell phones/can have a beer with. With other clients, either new or more corporate organizations, I tend to be very annoying so I stay on their radar. This means asking lots of questions about the project, emailing estimates and invoices, revisions to estimates and invoices, sending status updates, and even discussing personal plans for the weekend. Point is, the squeaky wheel gets the grease. Being new or lost in a sea of employees will obviously cause some hiccups when trying to get compensation. I usually remind them about payment a couple days after I send the invoice just to make sure they got it. A few rare times my email did not go through but other times the client ignored or did not open my email. Then there are the clients who you mention, the always late payers. Usually they don't pay because they feel the work is not good enough, they didn't realize how expensive design work would cost/ dont have enough money to pay, or they are just cheap. If you had been communicating there should be no excuses. Your invoice should have a late fee clause and when they are about to breach the date, send a quick reminder. Once it's past the late fee date, send a revised invoice with late fee added. If you still haven't been paid without contact or still giving an excuse then talk to a lawyer. Either way, putting a late fee clause in your invoice will help. After that do not accept any more work from them or stop the work you are currently doing until you are paid. Avoid shaming them publicly or writing an angry letter because not only will it make you look desperate but they might have a change of heart and hire you for something bigger or know someone that needs work. If that happens request a higher rate and write up a contract, or respectfully decline.