We purchased products off of a company for well over 30 years. Our business terms were 2% net 20 days. Now all of a sudden they want to switch the terms to Net 30 days. We were never consulted nor notified in any way. They just changed the terms on an invoice. Is that legal?
Business Payment terms
It is legal. It's your choice to buy from them on their terms.
One of my pet peeves is when customers want to dictate the term of payment. Negotiation is one thing, but dictating terms to a vendor is different. That vendor of yours may have had an increase in costs and wanted to keep your price the same. Taking away the discount is one way to do that.
its also a way to increase your price to the customer without announcing a price advance like everyone else in the business.