As of May 16, 2016, all products, Google Shopping requires GTINs for brand name products sold by multiple merchants. Google Product Feeds must now not only have GTINs, but Google is will be testing the accuracy of the data provided by manufacturers. Google has begun showing item-level warnings in the Diagnostics tab in Merchant Center for products that are missing or have the wrong GTIN.
This mandatory requirement is for products being sold to: Australia, Brazil, the Czech Republic, France, Germany, Italy, Japan, the Netherlands, Spain, Switzerland, the UK or the US.
Click here to read Google’s Merchant Center Help page regarding Unique Product Identifiers through GTINs.
Google GTIN Resources
For additional information on UPC/EAN EAN numbering and barcode requirements please visit www.gs1-us.info