RICHMOND, Va. — Lawmakers in Virginia moved forward Thursday with legislation that could make it the first state in the country to allow parents to block their children from reading any books in school if they contain sexually explicit material.

Opponents call it a slippery slope toward book banning; advocates say it's a parent's right to control their children's exposure to media, even if the books are considered classics.

It all started with Laura Murphy, a Fairfax County mother who said she was horrified to discover that one of her sons, a high school senior, was assigned to read the 1988 Pulitzer Prize-winning novel "Beloved."

The seminal work of fiction about a former slave after the Civil War by Nobel Laureate Toni Morrison contains scenes of bestiality, gang rape and an infant's gruesome murder, according Murphy, who said it could be inappropriate for young readers. She ticked off other critically acclaimed works in the same category: "The Bluest Eye," also by Morrison, "Invisible Man" by Ralph Ellison and "The Road" by Cormac McCarthy.

Under the bill, K-12 teachers would be required to "directly identify the specific instructional material and sexually explicit content contained in such material." Parents could "opt out" their children from reading material the parents found objectionable, and the teacher would have to find the student something else to read.

Schools follow a similar procedure for sexual education class, Murphy said.

"It just stands to reason when walking across the hall to English class, to be consistent, the same policies should apply," she said.

After a spirited debate in a Senate committee Thursday, it passed, 9 to 6, along party lines except for Lynwood W. Lewis Jr., D-Accomack.

Sen. Charles "Bill" Carrico, R-Grayson, said he had not read "Beloved," but based his opinion on excerpts, which he called evil enough to poison the minds of young people.

"Evil is just — when you plant the seed it's a kitten," he said. "You feed it, it becomes a lion and it eats you."

But Sen. Janet D. Howell, D-Fairfax, said she re-read the book over the weekend and praised Morrison for her place in the pantheon of American novelists.

"I think it's a slippery slope that's icy," she said. "Great literature is great because it deals with difficult human conditions. Not because it's easy."

Earlier this month the bill sailed through the House with unanimous support of Republicans and Democrats and no floor debate — an indication that most lawmakers were unaware of the potential for controversy.

On Monday the bill has a good chance of passing the Senate, where Republicans have a one-vote advantage, if Republicans stick together and Lewis maintains his support. In that case, House lawmakers would get another chance to voice any objections before it reaches the desk of Gov. Terry McAuliffe (D). His spokesman, Brian Coy, declined to say if McAuliffe would veto the bill.

While some individual schools and school districts around the country have taken steps to remove "Beloved" and other novels from class reading lists, this appears to be the first attempt by a state legislature to regulate curricula in this way, said James LaRue, director of the office for intellectual freedom at the American Library Association.

LaRue, whose organization tracks such legislation, said the Virginia bill could become a model for the nation.

But he said the approach could give the false impression that the most important thing about a particular work of literature is its sexual content. In that case, Shakespeare's "Romeo and Juliet" becomes nothing but "teen sex and suicide," LaRue said.

"The focus of this effort might be to discourage the use of this book altogether — and that's the chilling effect," he said, adding that his association nevertheless believes parents have the right to decide what their children read.

Millie Davis, director of the Intellectual Freedom Center at the National Council of Teachers of English, said parents have gotten used to ratings on movies, based on instances of profanity and violence, but books have to be considered for their educational value.

"Whatever happened on page 32 of a book is not why the book was chosen," she said.

In a letter to senators who voted Thursday, the National Coalition Against Censorship and like-minded organizations said public schools are can't discriminate against an idea simply because society finds the idea disagreeable. Signaling out the "over-inclusive and vague" standard of sexually explicit content also creates a problem, the groups said.

"Under this standard, titles as varied, valuable, and time-honored as Anne Frank's 'The Diary of a Young Girl,' Geoffrey Chaucer's 'The Canterbury Tales,' and most works by William Shakespeare could be flagged."

Del. R. Steven Landes, R-Augusta, chairman of the House education committee, sponsored the legislation at the request of House Speaker William J. Howell, R-Stafford.

"My job is not to judge the literature, it's just to provide the option to the parent," he said.

About half of Virginia school districts already require teachers to give parents advanced warning of "potentially sensitive or controversial materials in the classroom," according to a 2013 survey by the state Department of Education.

Murphy's initial effort to remove "Beloved" from Fairfax County classrooms in 2013 was unsuccessful, but she said a new superintendent was sympathetic and agreed to change the school district's policy, and parents are now notified of sexually explicit books.

In the meantime, Murphy took her cause to the state Board of Education, which began the slow process of considering amending state regulations. While she waited for her idea to clear procedural hurdles, Murphy said she lobbied lawmakers.

Landes said it would be up to the state Board of Education to write guidelines — including the tricky task of defining "sexually explicit" — for school districts to comply with the legislation if it becomes law.

LaRue said he worried that teachers could find the process so difficult that they decide not to teach certain books anymore.

Asked about that concern, Landes said: "That's up to them."