The Philippine government on Friday announced that U.S. Sens. Dick Durbin (D-IL) and Patrick Leahy (D-VT) have been banned from visiting the country due to “interfering with our processes as a sovereign state,” as Philippine presidential spokesman Salvador Panelo put it. More specifically, Durbin and Leahy have been involved in the case of incarcerated Philippine Sen. Leila de Lima, who they regard as a political prisoner.

De Lima, 60, is a member of the opposition and a prominent critic of Philippine President Rodrigo Duterte’s war on drugs. She was detained in February 2017 on charges of taking bribes from drug dealers when she served as justice secretary under Duterte’s predecessor.

De Lima and her supporters, including some major international human rights groups, believe she was jailed on false charges to suppress her criticism of Duterte.

“This is farcical. The charges are a total, absolute lie and fabrications,” De Lima told Al Jazeera in a jailhouse interview in December 2018.

“I am a victim of political persecution, and my right to due process has been violated,” she said, accusing Duterte of attacking her “honor, dignity, and womanhood” because he “hates strong women who stand up to him and fight him.”

De Lima, like the human rights organizations that support her, was strongly critical of the huge death toll in Duterte’s drug war, which has claimed up to 27,000 lives according to some estimates. De Lima has called for an international investigation of the drug war, a prospect Duterte loathes.

Duterte is furious with Durbin and Leahy because they added a provision to the 2020 U.S. federal budget that could bring sanctions against any Philippine official involved in the arrest and incarceration of De Lima. The budget was signed into law by President Donald Trump on Monday.

Panelo described Durbin and Leahy as “imperious, uninformed, and gullible” when announcing they were banned from entering the Philippines. He insisted De Lima’s detention was “lawful” and her case “not one of persecution but of prosecution.”

De Lima has named Duterte himself, and his spokesman Panelo, as among the dozen people directly responsible for putting her in detention.

The Duterte administration threatened to begin requiring visa applications from all Americans if the U.S. government bars any of its officials from entering the United States. Americans are currently able to visit the Philippines for up to 30 days without applying for a visa.