Mathias Dopfner, chief executive of Axel Springer, says his company is afraid of Google and its power.
He also asks in the letter, addressed to Google boss Eric Schmidt, whether Google intends to create a superstate where anti-trust and privacy laws don't apply.
Google has not commented on the letter.
Axel Springer publishes more than 200 newspapers and magazines including German papers Die Welt and Bild. It also has a significant online presence and television and radio interests.
Mr Dopfner's letter was published in Germany's Frankfurter Allgemeine Zeitung newspaper - which is not published by his company - in response to a column by Google's executive chairman Eric Schmidt.
Mr Schmidt's column had referred to the advertising relationship between Axel Springer and the search company. He described how the relationship had been challenging at times but how now they had "walked down the aisle" and signed a multi-year deal.
Mr Dopfner acknowledged that he was pleased at the marketing relationship between the two companies and an admirer of Google's entrepreneurial success but went on to say that the company had little choice but to engage with Google as "we know no search engine alternative to increase our online reach".
Global monopoly
The company makes 62% of its profits from digital business, he said, and the internet is a great opportunity, but he explained that he was concerned about the role Google plays online.
He referred to a long-running dispute between Google and the European Commission, which involved accusations that the search company gave favourable treatment to its own products in search results.
Mr Dopfner said the resulting agreement between the two parties was not a compromise but instead the Commission had "sanctioned the introduction of a business model, which in less honourable circles is called extortion".
Mr Dopfner went on to say in the letter that large technology companies like Google are far more powerful than people realise.He said the agreement would still allow Google to discriminate against competitors in search results. At the time Google said its proposals to change the way search results were ranked were fair and wide-reaching.
"With the exception of biological viruses, there is nothing with such speed, efficiency and aggressiveness that spreads like these technology platforms, and this also lends its creators, owners and users with new power."
He compared the company to the state monopolies that ran the German postal and telecoms services: "Today there is a global network monopoly. Therefore, it is of utmost importance that there are transparent and fair criteria in Google's search results."
Superstate
Mr Dopfner's comments were not just restricted to Google - the founder of social network Facebook also came under fire. He explained that he'd been at a conference when someone asked Mark Zuckerberg how Facebook stored data and protected users' privacy.
"And Zuckerberg said: 'I do not understand your question. Those who have nothing to hide, have nothing to fear.'
"Again and again I had to think about this sentence. It's terrible. I know it is certainly not meant that way. This is a mindset that was fostered in totalitarian regimes not in liberal societies. Such a sentence could also be said by the head of the Stasi or other intelligence service or a dictatorship."
Turning his attention to Google founder Larry Page, Mr Dopfner said: "He dreams of a place with no privacy laws and without democratic accountability."
Referring to comments Mr Page had made about the company wanting to develop ideas but being unable to because they were illegal, Mr Dopfner said: "Does this mean that Google is planning to operate in a legal vacuum, without the hassle of anti-trust and privacy? A kind of superstate?"
He finished the letter with a warning to Google that in the history of economics monopolies do not survive long.