BRUSSELS (Reuters) -Alphabet's Google was hit with an EU antitrust investigation into its spam policy on Thursday following complaints from publishers who say it has hurt their revenues, putting the U.S. tech giant at risk of yet another hefty fine.

Google began cracking down against companies gaming its search algorithm to push up rankings for other sites in March last year.

Its site reputation abuse policy targets the practice of publishing third-party pages on a site in an attempt to abuse search rankings by taking advantage of the host site's ranking signals, commonly referred to as parasite SEO.

The European Commission said its monitoring indicated that Google is demoting news media and other publishers' websites and content in Google search results when those websites include content from commercial partners.

It said Google's policy appears to directly impact a common and legitimate way for publishers to monetise their websites and content.

"We are concerned that Google's policies do not allow news publishers to be treated in a fair, reasonable and non-discriminatory manner in its search results," EU antitrust chief Teresa Ribera said in a statement.

"We will investigate to ensure that news publishers are not losing out on important revenues at a difficult time for the industry, and to ensure Google complies with the Digital Markets Act (DMA)," she said.

TECH GIANT CALLS EU INVESTIGATION 'MISGUIDED'

Google pushed back against the EU competition enforcer, saying the EU move risks degrading the quality of search results.

"The investigation announced today into our anti-spam efforts is misguided and risks harming millions of European users," Pandu Nayak, chief scientist at Google Search, wrote in a blog post.

"And the investigation is without merit: a German court has already dismissed a similar claim, ruling that our anti-spam policy was valid, reasonable, and applied consistently," he said.

He said Google's anti-spam policy helps level the playing field to thwart websites from using deceptive tactics to outrank websites competing on the merits with their own content.

German media company ActMeraki in April complained to the Commission, saying that Google's spam policy penalises websites.

The European Publishers Council, the European Newspaper Publishers Association and the European Magazine Media Association also have voiced similar grievances.

The EU investigation is under the DMA which seeks to rein in the power of Big Tech where violations can cost companies as much as 10% of their global annual sales.