WASHINGTON, Oct 18 (Reuters) - About a dozen U.S. senators from both parties on Monday formally introduced a bill that would bar Big Tech platforms, like Amazon (AMZN.O) and Alphabet"s (GOOGL.O) Google, from favoring their products and services. read more The bill follows others introduced with the goal of reining in the outsized market power of tech firms, including industry leaders Facebook (FB.O) and Apple (AAPL.O). Thus far none became law, although one, which would increase resources for antitrust enforcers, passed the Senate. read more Senators Amy Klobuchar and Chuck Grassley"s bill would prohibit platforms from requiring companies operating on their sites to purchase the platform"s goods or services and ban them from biasing search results to favor the platform. A companion has passed the House Judiciary Committee. It must pass both houses of Congress to become law. Reuters reported on Wednesday, after reviewing thousands of internal Amazon documents, that Amazon"s India operations ran a systematic campaign of creating knock-offs and manipulating search results to boost its own private brands in the country, one of the company’s largest growth markets. read more When news of the bill broke last week, both Amazon and Google warned of potential unintended consequences. Amazon said in a statement that the bill, if it became law, "would harm consumers and the more than 500,000 US small and medium-sized businesses that sell in the Amazon store, and it would put at risk the more than 1 million jobs created by those businesses." Google said that the measure would make it more difficult for companies to offer free services -- Google"s search and maps are both free -- and would make "those services less safe, less private and less secure." Facebook, which said that it competes with a range of social media, including TikTok and Twitter, said antitrust laws should "not attempt to dismantle the products and services people depend on." Klobuchar chairs the Senate Judiciary Committee"s antitrust subcommittee while Grassley is the top Republican on the full committee. Co-sponsors include five Democrats and five Republicans. Companies expressing support for the bill included Spotify, Roku, Match Group and DuckDuckGo, Klobuchar"s office said in a statement. The bill would not break up the companies or force them to drop services but bars some bad behaviors that affect businesses that rely on their platforms, said Stacy Mitchell with the Institute for Local Self-Reliance who said that she would prefer a more aggressive bill.