The investigation is at a preliminary stage so it could be lobbied away, but it means Google's anti-trust woes are getting closer to home. 

Google does not directly profit from the mobile operating software, which is installed on the vast majority of smartphones and in the US there is strong competition from Android. Instead it requires users to install some of its services onto the "home page."

Regulators are looking at whether Google unfairly uses the software to promote its other dominant services.

In recent months, a number of mobile application makers have complained to the Justice Department that the "home-screen advantage" makes it all but impossible for them to compete.

The FTC has worked out an agreement with the Justice Department to investigate the claims, the people involved in the inquiry said.

Google might get away with this in the US.  There is competition and phone companies do not have to use Android. The fact that Google does not make money directly from Android might help too. . Google also spends a lot of dosh on lobbying.  Things are less likely to go so well for it in the EU where it is facing a similar problem..