The search engine giant informed sellers that the terms and conditions of Google Shopping have been altered to omit items that violate its "culture and values".
Google said in a statement: "Our Company has a strong culture and values, and we've chosen not to allow ads that promote products and services that are incompatible with these values."
The move was met with opposition from American gun advocates, who have started a petition on Change.org claiming violation of the Second Amendment.
"This has started to severely affect many people's ability to find good prices on things ranging from knives to swords to hunting rifles and ammo, to axes," the petition organisers claim. "Why does Google feel the need to tell people they cannot shop online for legal items?
"If you wish to purchase a gun, you are required to do a background check… The new policy will only effectively disable many law-abiding citizens from acquiring legal weapons for legitimate purposes at reasonable prices, and hurt many, many small business's income."
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Google has issued an apology to its merchants and users affected by the policy change, claiming that the decision was reached after lengthy consideration.
The company also announced plans to introduce sponsored listings to its shopping results, according to The Telegraph.