If you are subject to the new "Sugary Drinks Tax" (or even if you are not) the first returns or opt outs are due on 4/30/18.
You or your business may have gotten a notice from the County and City of San Francisco regarding the new Sugary Drinks Tax aka "Soda" tax. This relates to ballot measures that passed back in 2016. Certain businesses (a lot of retailers) are exempt from the tax so be sure to check with your CPA or Accountant.
Even though the tax is commonly referred to as a "soda" tax there are a lot of drinks that are subject to the tax. The San Fransisco Ordinance list includes nonalcoholic "beverages commonly referred to as “soda,” “pop,” “cola,” “soft drinks,” “sports drinks,” “energy drinks,” “sweetened ice teas,” or any other similar names." Excluded from the tax are natural juice/vegetable drinks, any milk product (vegan and non-dairy products are included), and beverages for medical use.
You can read the full ordinance here
FAQ can be found here