LONDON (Reuters) - Google parent Alphabet has urged a London tribunal to block a mass lawsuit which accuses it of abusing its dominance in the online advertising market, in the latest case to focus on the search giant's business practices.

The lawsuit seeks damages of up to 13.6 billion pounds ($16.9 billion) on behalf of publishers of websites and apps based in the United Kingdom, who say they have suffered losses due to Google's allegedly anticompetitive behaviour.

Lawyers for Ad Tech Collective Action asked the Competition Appeal Tribunal (CAT) to certify the case to proceed towards a trial at the start of a three-day hearing on Wednesday.

Google, however, said the case was incoherent and did not explain how alleged anticompetitive conduct had supposedly caused losses to the publishers.

Ad Tech Collective Action's lawyer Robert O'Donoghue said the London lawsuit was "the latest in a series of major set-preferencing abuse cases involving Google".

The case comes amid ongoing probes by regulators into Google's adtech business, including by Britain's Competition and Markets Authority and the European Commission, which O'Donoghue said was concluding imminently.

O'Donoghue also referred to two multibillion-euro fines levied on Google by the European Commission, over its online shopping search service and the requirement to pre-install Google Search and its Chrome browser on Android mobile devices.

Google is also fighting two lawsuits in the U.S., one brought by the Department of Justice and another by Texas and other states, accusing the company of anticompetitive conduct.

The company "strongly rejects the underlying allegations against it", its lawyers said in court documents for the CAT case. "Google's impact in the ad tech industry has been hugely procompetitive."

Ad Tech Collective Action's proposed lawsuit is the latest against a tech giant at the CAT, which already this year has certified a $3.8 billion case against Facebook parent Meta and a nearly $1 billion case against Apple ( AAPL ).