The collection of non-payment of commercial debt is generally covered by law. Legal frameworks exist in some countries that dictate terms relating to when a payment is considered “late” and the kinds of fee, penalty and late payment interest that can be levied to recoup the additional debt collection costs. However, these laws are not applied worldwide.
Your chances of recovery are better if you trade in North America or Europe. For example, the US, UK, Netherlands and Scandinavia have legal frameworks covering late payments. In the UK, the Late Payment of Commercial Debts (Interest) Act 1998 and its 2013 amendment entitle suppliers to collection costs incurred as well as a late payment interest at 8% above base rate of the Bank of England.
Keep in mind that debt collection and its application vary widely from country to country. Some entire regions have no legislation to support suppliers. Late payment letters may be ignored. Croner’s Reference Book for Exporters is a useful resource for information on trade practices, as are our country reports and collection profiles available here.