The Fair Trade Commission investigated Google Korea this week by sending its inspectors to the headquarters, marking the fourth antitrust investigation including a raid last September.

While the regulator’s raid on Google’s Korean unit in southern Seoul was the result of a joint-complaint by local Internet portals it is alleged the U.S.-based tech giant hindered the FTC from conducting an ordinary probe.

The allegation of obstructing civil servants’ on-the-spot investigation could yield an intensive probe and stern punitive action the FTC, according to market observers.

The Google Seoul office initially under antitrust investigation last September for allegedly seeking monopolistic status among search engines in contracts with smartphone manufacturers.

NHN and Daum Communications have continued to argue that Google Korea has instructed smartphone manufacturers not to include applications provided by Korean search engines.

They claimed that Google Korea had pressured the smartphone companies to include only Google Search or its own applications on Android-powered devices.

An FTC official said the probe is focused on the issue of whether the company sought to abuse its power as the world’s largest search engine in the smartphone application market.

Another issue is that the Google Korea unit has been suspected of concealing related documents and hampering inspectors’ on-the-spot probe.

Aside from the allegations involving the antitrust rules, the FTC is likely to widen the scope of its inquiry as to whether the practice is a violation of the civil servants law, according to market observers.

Google denied the allegation even though it promised to cooperate with the investigation of the Korean regulator.

“We will work with the KFTC to address any questions they may have about our business,” a Google spokesperson was quoted as saying by a local news provider.

The spokesman said that Android is an open platform and carrier and OEM (original equipment manufacturer) partners are free to decide which applications and services to include on their Android phones.

Last year, Google came under investigation by U.S. and European antitrust regulators.

As the investigation came following Google’s purchase of Motorola Mobility in August 2011, industry sources expected that worldwide regulatory pressure on the search giant would get more severe.

FTC senior officials said that the Google Korea issue could greatly affect the Korean economy.

By Kim Yon-se (kys@heraldcorp.com)