"By creating a new paid offering, we'll generate a new source of revenue that will supplement your fast growing advertising service," the letter said.
Google introduced a subscription-style music service within YouTube in November, and has been trying to boost original content on the video website, which has more than 1 billion monthly viewers. With ad-free subscriptions, Google is moving closer to competing with streaming services, including the new HBO Now.
YouTube will offer all the same videos without ads for a monthly fee, which hasn't been set yet, according to the note. The service is also likely to include offline access.