The US Department of Justice (DoJ) reportedly prepared to file a second antitrust lawsuit against Google, potentially adding to pressure on the search giant to reform its advertising business.

Bloomberg reported regulators stepped-up an investigation of Google’s digital advertising business, with plans to potentially file the latest lawsuit this year.

The DoJ filed a suit in 2020 accusing Google of monopolising the search and advertising markets, while a group of 35 US states also took action some months later.

During testimony to the US Senate given prior to those lawsuits, Google president of global partnerships and development Donald Harrison argued the fact prices for online adverts had been falling showed the market was competitive.

Advertising accounts for more than 80 per cent of revenue for Google parent Alphabet.

European regulators have also accused Google of unfairly dominating the search ad market.

In June, Google settled an investigation by France’s competition authority by agreeing to pay a €220 million fine and share more data with publishers.