The European Union has sent advertisers a lengthy questionnaire as part of its anti-trust investigations into whether Google's online marketing services break competition laws.
The 120-question document will look to determine whether the company manipulated its search results and used its popularity to hinder the activities of rivals, the New York Times reports.
Marketers will be asked such things as whether the firm ever suggested an increased advertising spend would improve their results in natural search.
"Please explain whether and, if yes, to what extent your advertising spending with Google has ever had an influence on your ranking in Google’s natural search," is another question that advertisers will be asked to respond to, according to the newspaper.
The European Commission opened an investigation into Google last year following complaints from web companies based in France, Germany and the UK.
Commenting on the report, Search Engine Land's Greg Sterling observed that "a sceptic might call it a fishing expedition".
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