Last Fall, Google Shopping began requiring feeds targeting Australia, Brazil, Czech Republic, France, Germany, Italy, Japan, Netherlands, Spain, Switzerland, the United Kingdom or the United States to submit valid GTIN and brand information for over 50 brands.

The company recently announced the expansion of GTIN requirements beyond those 50 brands to include all products with a GTIN assigned by the manufacturer.

Earlier this week, Google began giving merchants item-level warnings in the Diagnostics tab for products that don’t meet the requirements. Enforcement will begin on May 16 (h/t: Search Engine Land).

At this point, merchants will begin seeing item-level disapprovals in the Diagnostics tab, and will have to meet the GTIN requirements to continue serving ads for products.

“GTINs help us understand exactly what you’re selling,” Google says. “When we understand what you’re selling, we can help boost your ad performance by adding valuable details about the product and serving the ad in a more relevant way to users. This also means that your ads can serve in more places on Google, YouTube, and our partner sites. Merchants who’ve added correct GTINs to their product data have seen conversion rates increase up to 20%.”

“If you sell brand-name products that are sold by multiple merchants, you should take a close look at the new requirements and double check that your product data is correct and up to date, ” it says. “If you sell used, custom, handmade, or vintage products, this change probably won’t impact you. You can still improve your ad performance by adding unique product identifiers to your product data where they’re available.”

More details about the GTIN requirements and unique product identifiers are available here.

Image via Google