The government of Cambodia has formally exiled the country’s opposition leader, Sam Rainsy, ordering immigration officials to “take legal action to prevent this person from entering Cambodia.” A letter from the country’s Cabinet to immigration officials, made public over the weekend, also warns that planes with him aboard will be forced to turn around and leave, according to local news site the Khmer Times. Sam Rainsy, president of the opposition Cambodia National Rescue Party (CNRP), has been in self-imposed exile in France since late last year. He is wanted on criminal defamation charges dating back several years — in a widely viewed as politically motivated — but had nonetheless resolved to return to Cambodia in time for general elections slated for 2018. Fellow CNRP lawmaker Mu Sochua claims that banning the party’s leader from entry is unconstitutional, and violates several international conventions to which Cambodia is party, including the Universal Declaration of Human Rights and the International Covenant on Civil and Political Rights. A leading human-rights lawyer, Sok Sam Oeun, said the ban lies in a legal “gray area” because of Sam Rainsy’s dual nationality as both French and Cambodian.