BRUSSELS (Reuters) -Alphabet unit Google and digital advertising firms were hit with fresh privacy complaints to national watchdogs in six EU countries on Thursday over the way they sell ads to potential advertisers through a bidding process. Since 2018, complaints have been filed in 15 EU countries over real-time bidding systems, the core of today’s online advertising industry, for allegedly breaching Europeans’ privacy rights. The method, which collects people’s browsing history and broadcasts it to hundreds or thousands of companies so they can auction and place ads, is used by Google and member companies of the Interactive Advertising Bureau (IAB), a standards and lobbying group for the online advertising industry with more than 650 members. Browsing history may reveal intimate personal data and consumers’ consent is not sought in some cases. The Berlin-based Civil Liberties Union for Europe, the UK-based Open Rights Group and freedom and human rights group the Panoptykon Foundation coordinated complaints from digital and human rights groups in Croatia, Cyprus, Greece, Malta, Portugal and Romania to their national privacy watchdogs. “Today, more civil society groups are saying enough with this invasive advertising model and are asking data protection authorities to stand up against the harmful and unlawful practices they use,” Orsolya Reich, Liberties’ senior advocacy officer, said in a statement. The group urged the privacy bodies in the six countries to team up with lead supervisory bodies in Ireland and Belgium, which are looking into similar complaints. “A joint investigation is necessary here, as real-time bidding functions in the same way across borders and produces the same negative effects in all EU member states,” the group said. Google said it requires publishers to obtain consent for personalized advertising in order to use its systems. “We are engaging fully in the DPC’s active inquiry on real-time bidding. Authorized buyers using our systems are subject to stringent policies and standards,” a Google spokesman said. The IAB, which earlier this week rejected a preliminary report by the Belgian data enforcer, said it is not a data controller for real-time bidding systems and does not process any data. It said it was confident that its standard for its members to comply with the EU data protection rules known as GDPR offers greater transparency, choice and accountability in digital advertising.