SARS accused Pauw of violating the law for revealing details of President Jacob Zuma's tax affairs.
Pauw is ready for the court battles.
"We face the potential of a multitude of legal challenges, both criminal and civil. If you read the book, you will realise that it is a tried and tested strategy of the state to legally [wear] out its enemies," he said.
The controversy has resulted in a massive boost to sales as curiosity about what government wants to hide soars.
Amazon rated the book a best seller and the Kindle edition leaped up the charts on Saturday to eighth fastest-selling e-book globally.
The book has been widely welcomed with many voicing their support, but some have questioned Pauw's motives.
"The President's Keepers cannot be banned because the right to express an opinion is guaranteed by the Constitution," tweeted COPE leader Mosiuoa Lekota.
The government, he added, was entitled to contest the correctness or otherwise of what was published, but if it does not, it does not have the right to silence the truth.