My business partner and I started a construction related business last year. We recently (August 2021) received payment for an invoice that was issued June of 2020. At that time we did not have any sort of policy in our invoices regarding late fees or interest. The client did not agree to any such stated late fees or interest policy, and my business partner thinks we can attempt to collect interest after the payment and without any upfront disclosure of this interest policy(because it didn't exist). I think this seems crooked and sleazy, and it seems like it wouldn't be legal. Does anyone have insight here? I am in charge of correspondence and don't feel comfortable trying to do this, but I have no idea whether or not either of us is justified. We recently created a clear policy on this matter, but at the time of invoicing we did not. Help is appreciated - thanks.
What does your contract say?
There is no common law right to interest on late payments and BC does not as yet have a statutory prompt payment regime which might create one. If you had commenced court action, there is a right to pre and post judgement interest, but you didn’t so there isn’t.
If your contract includes an interest rate to be charged on late payments then you are entitled to that.
Assuming that the contract (not the invoice - the invoice is not part of the contract) specified a time for payment (did it?) and it was paid after that then that is a breach of contract. If you have suffered damage as a result of not having this money (for example, if you had to borrow it from a bank) then you could sue for the costs directly attributable.