When writer Ilija Trojanov wasn’t allowed to board his Miami-bound plane on Monday, he was surprised. The Bulgarian-German author was in Brazil, in the middle of a trip that would bring him to an academic conference in Denver, and he had his visa to come to America in hand.

“I have not been allowed to travel to Iran, Tadjikistan and Kirkystan and now the USA,” he told The Times by email, “but the other three did not grant me a visa, so I just stayed at home, more comfortable than hanging out at Brazilian airports.”

Trojanov, who has been unable to find out why his entry was denied — or, for that matter, anything else from U.S. authorities — believes he was blocked because of his criticisms of surveillance by the National Security Agency, as revealed recently by former contractor Edward Snowden. He was one of the signatories to an open letter to Germany’s Chancellor Angela Merkel urging her to take a stance against the NSA’s mass online surveillance.

The award-winning author was born in Bulgaria in 1965; his family fled the country in 1971, soon finding political asylum in Germany. His father, an engineer, took the family to Kenya the next year; Trojanov spent nine of the next 12 years in Nairobi and the rest in Germany, where he also attended college.

He has published nonfiction books about Africa, written a novel of exile, and written about living in India, and performing the Hajj and penned a novel about Richard Francis Burton’s trek through Tanzania.

PEN protested Trojanov’s exclusion from the U.S., writing on its website that “this most recent act of ideological exclusion calls to mind our country’s checkered history of barring writers whose political views it disfavors, at a time when the need to model tolerance for dissent is stronger than ever.”

Germany’s foreign minister has contacted U.S. authorities requesting they “resolve this issue,” the Associated Press reports.

“The reaction of many colleagues, of the media and the German as well as US PEN have been supportive and exemplary,” Trojanov told The Times. “But it is important to note that my case is not unique but symptomatic of certain worrisome developments which explains the outcry.”