Denmark and the U.S. have been collaborating on security efforts through the National Security Agency (NSA) since the 1990s, according to newly released information.

Documents obtained by a Danish broadcasting company show that American officials put “significant pressure” on the European country to allow for communication surveillance, according to The Local, an English-language European news outlet. The documents also show that the Danish Defense Intelligence Service cooperated with the NSA to tap undersea internet cables.

The U.S. is said to have threatened Denmark, warning that the country would be excluded from the list of U.S.'s close allies if it didn't alter its encryption laws.

Whistleblower Edward Snowden initially exposed documents that highlighted Denmark's intimate security relationship with the U.S.