In Europe, this might be illegal: > Merchants operating in the European Union must give customers 7 business days’ notice before changing the price of their recurring billing plan; 7 business days’ notice is also required before billing customers if it has been 6+ months since their last payment. If you don’t operate in the EU, these notices aren't required (but they're still good practice).

From: https://articles.braintreepayments.com/guides/recurring-bill...