Those companies, Foundem in particular, have long complained that Google penalized their Web sites in search results under competitive pressure.

Google confirmed that it has received an inquiry from European regulators but denied any wrongdoing. "While we will be providing feedback and additional information on these complaints, we are confident that our business operates in the interests of users and partners, as well as in line with European competition law," the company said in a blog post.

It seemed like only a matter of time before a major regulatory agency opened a formal review of Google. The company has faced extreme scrutiny over the past several years as it has come to dominate the Internet. Google's share of the search and search advertising markets in Europe is even higher, around 90 percent, than it is in the U.S., where Google has come to know its regulatory counterparts quite well during the first year of the Obama administration.