On Sept. 30 the German author Ilija Trojanov was checking in for an American Airlines flight from Salvado de Bahia, Brazil, to Miami, en route to Denver, when he ran into trouble.

“I gave the agent my passport as usual, and there must have been something on the screen, because that moment she stood up and disappeared,” he recounted in an interview with Slate.“Her superior came in and claimed that because of cross-border security, she was obliged to inform the American authorities that I was trying to check in and she wanted to take my passport. After about 10 or 15 minutes, I asked the lady at the check-in counter if it was a regular thing. She said, ‘Your case is special.’ ” Shortly after that, without explanation, Trojanov was told he would have to return to Germany.

Trojanov, a Bulgarian-born writer known in Germany for his novels as well as nonfiction writing on contemporary European politics, had been attending a book fair in Brazil. He was heading to Denver to attend the America’s German Studies Association conference. He says he was particularly angered when the airport officials told him he would have to apply for a visa. German citizens don’t need visas to travel to the United States for business trips under 90 days, just an electronic authorization known as ESTA, which Trojanov says he had. In any case, acquiring a visa is an involved process that certainly couldn’t have been completed in time for him to make his conference.   

“Telling me to get a visa was the official version of saying ‘go and fuck off’ in this particular context,” Trojanov says.

This isn’t the first time the 48-year-old writer has had trouble traveling to the United States. Another time, he was initially denied a visa—again without explanation—to teach for a semester at Washington University in St. Louis. He did eventually receive a visa, only after the university wrote the State Department on his behalf  several weeks after the semester had begun. 

So why was he denied this week? The U.S. embassy in Berlin isn’t commenting on the case, but Trojanov suspects it might be because of how outspoken he has been about on U.S. government surveillance, particularly in light of recent revelations about the National Security Agency. In 2010, he co-authored a polemical book on surveillance titled Attack on Freedom: The Security Obsession, the Surveillance State, and the Dismantling of Civil Rights, which warns of the dangers of government surveillance in Europe.

More recently, he and his co-author Juli Zeh wrote an open letter to Chancellor Angela Merkel in the wake of Edward Snowden’s NSA leaks demanding that the German government “tell the nation the full truth about the spying offensive” carried out by the U.S. agency on German soil. 

The Pen American Center has protested his exclusion to an academic conference to the State Department, and the German foreign ministry has asked the U.S. government for an explanation.

But Trojanov isn’t optimistic that they’ll get one. “I’m quite certain that I’m not going to receive any information,” he says, noting that the last time he tried to find out why he was denied entry he was told, “We do not give out any information regarding reasons for this process.”

“If they’re not going to give the German government any information regarding [the NSA surveillance], why should they bother with such a minor matter as my own?” he asks.

Trojanow ended up speaking at the conference via Skype, but he still plans to apply for a U.S. visa. “I’m prepared to fly to New York and be sent back just to find out how this works and what’s happening,” he says.

While frustrated by the experience, he says he’s been happy to see German public opinion shifting on the issue of government surveillance. “When my co-author and I published this book in 2010, many reacted in an incredulous way,” he says. “They said we were exaggerating or being paranoid. They called us conspiracy theorists. People are coming to realize that this is very real and are coming to understand the extent of the threat.” 

He sees the attention his case has gotten, which has included extensive print, radio, and television coverage in Germany, as evidence of this shift. “The fact that my case, which I don’t think was that dramatic, provoked such a huge media frenzy was surprising,” he says. “My case doesn’t warrant that kind of attention. The only explanation for it is that people have been frustrated by what we’ve learned about the activities of the NSA and are frustrated by the fact that there’s nothing they can do about it.”

If Trojanov really was excluded from the United States because of his political views, it seems like a pretty short-sighted strategy. His three-year-old polemic on surveillance is currently the fourth-best-selling politics book on Amazon in Germany.