SAN FRANCISCO (Reuters) - Alphabet Inc’s Google sought to ease online publisher concerns on Thursday about the effects European data privacy rules going into effect in just a few hours will have on their ad business.

FILE PHOTO: Silhouettes of laptop and mobile device users are seen next to a screen projection of Google logo in this picture illustration taken March 28, 2018. REUTERS/Dado Ruvic/Illustration/File Photo

Under the General Data Protection Regulation (GDPR), the biggest overhaul of data privacy laws in over 20 years, organizations must have transparent justification for processing personal data, starting Friday.

The rules threaten fines of as much as 4 percent of company revenues for violations, although attorneys and European Union officials have cautioned there will be a grace period.

But that has not prevented an anxious scrambling this week as companies seek and interpret last-minute counsel from consultants, business partners and regulators.

Google officials, speaking on Thursday to 70 media and advertising firms at its New York City office and on a private telecast, described compliance efforts as a work in progress and said the company would release additional tools to assist publishers in June and August, according to a person with direct knowledge of the discussion.

Internet companies that track users online, whether for shopping, banking or other reasons, are set to face significant scrutiny.

The new rules require that they have specific justification, such as consent, for using personal information.

The worst case for Google and advertisers would be users refusing to allow sharing of their personal data. Some ads they encounter would no longer be personalized to their interests, and if clicked on less, could cut industry spending.

British attorney Gabriel Voisin, whose firm Bird & Bird revised 500 online privacy policies over

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