Beijing (AP) — Ahead of President Donald Trump’s visit to Beijing, literary luminaries such as Margaret Atwood and Philip Roth are calling on China to free the widow of Nobel Peace Prize winner Liu Xiaobo.

A letter issued through the writer’s organization PEN America asks that China remove restrictions on Liu Xia’s freedom of movement and allow her to meet freely with whomever she wishes.

“Liu Xia has undergone great suffering for many years, simply for being the wife of a man that China has deemed to be a dissident,” the letter said. “She should be free to meet freely with family, friends, and members of the international community, free to travel where she wishes, and free to be reunited with the outside world.”

Others signing the letter include Chimamanda Adichie, Louise Erdrich, Robert Pinsky and Stephen Sondheim.

In a news release last week, PEN America’s executive director, Suzanne Nossel, said the writers hope Trump will “voice the United States’ concern about the inhumane and unjustifiable detention of a poet who has been accused of no crime.”

An accomplished poet and artist, Liu Xia has been under unofficial house arrest since Liu Xiaobo was awarded the 2010 prize while serving an 11-year prison sentence for incitement to subvert government power resulting from his co-authoring a manifesto calling for political reform. Her whereabouts since his July 13 death of liver cancer are unclear.

China has dismissed all previous calls for her freedom, including from the United Nations’ human rights chief.

Trump arrives in Beijing on Tuesday for talks with Chinese President Xi Jinping, who has overseen a wide-ranging crackdown on civil liberties under the strict authoritarian rule of the Communist Party.