On Sunday, the Danish Atlantic Council cancelled its upcoming conference celebrating NATO’s 70th anniversary after the U.S. embassy in Copenhagen barred a critic of President Donald Trump from attending the event.

“After serious consideration, we have decided not to proceed with the Conference,” Dr. Lars Bangert Struwe, the council’s secretary-general, said in a press release. “The progress of the process has become too problematic; and therefore, we cannot participate in the Conference, let alone ask our Speakers to participate.”

Stanley Sloan, a foreign policy expert who has criticized Trump, was slated to give remarks at the conference on December 10. However, the council stated that U.S. Ambassador to Denmark Carla Sands, a Trump appointee, had “demanded” that Sloan be uninvited.

The embassy’s official Twitter account claimed on Sunday that the embassy “supports freedom of speech,” and said the event cancellation was “unfortunate.”

“Mr. Stanley Sloan’s proposed last-minute inclusion in the program by

@AtlantDK did not follow the same deliberative process of joint decision-making and agreement that we followed when recruiting all other speakers,” the embassy tweeted.

“I’m sorry that you objected to my inclusion in the conference,” Sloan responded. “I am an experienced public diplomacy lecturer who always represents his country well.”

The NATO policy expert, who said he was “stunned” by the decision, has posted his speech online.