The American Civil Liberties Union is entering the escalating battle in Watauga County over whether the school board should ban a book from the high school curriculum.

Just days after several teachers reported receiving letters they considered “threatening,” the ACLU announced it will join a community rally Thursday afternoon, hours before the school board is scheduled to vote on the issue.

“We’re proud to join students and parents from Watauga County in urging their local officials to do the right thing and not go down the slippery slope of banning books that promote critical thinking and classroom dialogue,” said Chris Brook, legal director of the ACLU-NC Legal Foundation.

At the center of the controversy is “The House of the Spirits,” written in 1982 by Chilean author Isabel Allende. According to numerous reviews, the book tells the story of four generations of a family that deals with social revolution and a spirit-filled world.

Events in the book include rape and executions.

“The House of the Spirits” is part of the honors English curriculum for 10th-graders at Watauga High School, and several parents complained to the school board in September and October. Those parents said the book is too graphic for high school sophomores, and they asked the board to remove the book from the curriculum.

Watauga High officials say students are permitted to read “Moby Dick” instead, but some parents said students who opt out of reading “The House of the Spirits” are removed from mainstream class activities.

In recent months, according to school officials, two separate committees of teachers have voted to support keeping the book.

But High Country Crime Stoppers reported Monday that several teachers received letters that contained wording they considered “threatening.” Those letters mentioned the book controversy. Boone police say they are working with the school system to find the person or people who wrote the letters.

The school board is scheduled to meet at 7 p.m. Thursday at the Margaret Gregg Education Center in Boone.

The rally is sponsored by Appalachian State University’s Department of English, the student English Club and the ASU chapter of the honor society Sigma Tau Delta.

The rally is scheduled for 4 p.m. in the Table Rock Room in the Plemmons Student Union on the ASU campus.