Mark Hamlen wrote: All of my clients are within the EU and the EEC. Bank transfers are free of charge within these areas
This isn't quite so straightforward. There are generally bank charges for transfers, though some banks don't charge.
The SEPA (Single European Payments Area) rule is that cross-border transfers **between EUR-denominated accounts** in EU member states should not cost more than domestic transfers between EUR-denominated accounts, whereby this rule applies separately to the arrangements for the payer and the beneficiary. For example, if the payer's bank doesn't charge for EUR domestic transfers, but the beneficiary's bank does, then the payer won't be charged for cross-border payments, but the beneficiary will be charged.
so I was suddenly surprised when a UK client suddenly started paying out of their US office, which caused me to be hit with large bank charges (17 euros on each invoice paid). What would you do in this situation?
That's clearly unacceptable. What do the terms and conditions say? Who is your client (the UK company or the US company)? Note though that, as a rule, transfers from the UK to eurozone countries will only be relatively cheap (or potentially free for the beneficiary) if they're made from a euro-denominated account in the UK.
The standard business practice, incidentally, is for each party to bear its own bank charges.