Danish authorities on Wednesday charged a Russian national with espionage.
The man was accused of collecting and selling information on Danish energy technology to a Russian intelligence service, the Danish prosecution said in a statement.
The Danish Security and Intelligence Service (PET) conducted the investigation.
The unnamed suspect has been in pretrial custody since July, and if convicted risks up to six years in prison. Prosecutors want the man to be expelled after serving a possible sentence, the statement read.
Trial behind closed doors
The Russian embassy in Copenhagen issued a statement saying it considers "the arrest of our compatriot and the charges brought against him to be a mistake" and hopes for his release.
The trial is expected to be held behind closed doors. News agency Ritzau said the venue was likely to be the city of Aalborg in western Denmark. A trial date is pending.