Up until today, if you subscribed to an App Store service or app and enabled auto-renew, you would have to manually opt-in to a price hike before it affected you. While this meant that you had more control over your spending habits, it could also lead to interrupted services if you forgot to opt-in.
Apple thinks that this is not a desirable situation so it has now modified its subscription policies to allow developers to increase subscription prices in some cases without requiring you to manually opt-in and agree to the hike.
An announcement from Apple notes that auto-renewal without your prior approval is allowed under specific circumstances. Basically, if the price hike doesn't happen more than once a year and is not more than $50 or 50% of the annual subscription price, your explicit approval won't be required. For subscriptions with smaller durations, the threshold is set at $5 or 50% of the subscription price.
Although your explicit approval would not be required in these cases, Apple will still inform you of the hike via emails, push notifications, and messages within the app. However, if you somehow miss or ignore these and forget to cancel your subscription, you will be charged the increase rate at the start of your next billing period.
It is important to note that increased charges for subscriptions with auto-renewals only apply to those which fall within the aforementioned thresholds. Any that exceed them will still be required to get explicit approval from the user ahead of the next billing period.