Just as Google was working to settle the antitrust investigation launched by the European Union, the governing body has tacked on one more demand: change your mobile services too.

According to the Financial Times, EU Competition Commissioner Joaquin Almunia saved this final stipulation until settlement talks were already well into process. It's unclear what exactly Google needs to change but if the search giant doesn't concede it could lead to the settlement talks falling apart.

The EU's antitrust probe was opened in 2010 when European regulators asked the company to explain how it ranked search results and advertising after complaints of competitive behavior from European businesses. Throughout the course of the inquiry, Google has 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 when the investigation was launched.

After considerable investigation, Almunia announced in June that he was giving Google an ultimatum -- if the search giant didn't address the EU's antitrust concerns and show "concrete signs" of improvement by July, it would launch a formal complaint. Google listened and at the beginning of this month it offered Almunia a settlement proposal.

The settlement talks have been in the works the past couple of weeks, which initially only covered PC-based services. Almunia has said he prefers to settle but, according to the Financial Times, the negotiations are on "knife-edge" and the outcome will partially depend on whether Google agrees to change its mobile services too.

When contacted by CNET, a Google spokesperson said, "We continue to work cooperatively with the European Commission."

If the settlement talks fail, Google may be charged with a hefty fine of up to around $3.8 billion (a maximum of 10 percent of its $37.9 billion global revenue last year) and a continuing legal battle.

Updated at 11:00 p.m. PT with comment from Google.