Apple has been subpoenaed by the US Federal Trade Commission (FTC) to provide information regarding how it incorporates Google’s search technology into its mobile devices, according to Reuters sources.

The FTC has asked Apple to provide documents related to agreements made with Google to make its service the preferred search engine on the iPhone and iPad. Microsoft and other Google rivals have said these agreements with OEMs are anticompetitive and it is understood that the FTC has sent similar subpoenas to other handset makers and operators.

The FTC court order suggests it is taking a closer look at Google’s business practices with the details of its agreement with Apple likely to show if it is abusing its dominance of the search market to boost its mobile phone advertising revenue.

Antitrust lawyer at Brownstein Hyatt Farber Schreck LLP in Washington, Allen Grunes, told Reuters that as mobile search becomes more widely used, the default search service will become more significant.

The FTC started investigating Google around a year ago to determine whether it unfairly increases advertising rates for competitors and ranks search result to increase the prominence of its own businesses, such as the Google+ social network. The antitrust probe is also looking at whether Google is using Android to harm competition in the smartphone market.

Google has been the default search engine for the iPhone, iPad and iPod Touch since they were launched. Google Maps is also the favoured mapping service for the devices.