(NewsNation) — The American Library Association (ALA) is celebrating its “Banned Books Week” this week, where the organization celebrates the freedom to read books often affected by censorship attempts.

The number of books attempted to be restricted or banned before the start of this school year has more than quadrupled from just a couple of years ago, and experts believe these numbers could actually be much higher.

According to the ALA, there were 273 books challenged or banned in 2020, 377 books challenged or banned in 2019 and 483 books challenged or banned in 2018. In 2021, the association tracked 729 challenges to “library, school, and university materials and services” that affected 1,597 individual books.

The New York Times reported there have been 1,651 books affected by attempted bans or challenges so far this year in 2022.

Reports show that there have been more than 50 groups created in the U.S. that advocate for book banning in the last year.

Top 10 Most Challenged Books 2021:

1. “Gender Queer” by Maia Kobabe
2. “Lawn Boy” by Jonathan Evison
3. “All Boys Aren’t Blue” by George M. Johnson
4. “Out of Darkness” by Ashley Hope Perez
5. “The Hate U Give” by Angie Thomas
6. “The Absolutely True Diary of a Part-Time Indian” by Sherman Alexie
7. “Me and Earl and the Dying Girl” by Jesse Andrews
8. “The Bluest Eye” by Toni Morrison
9. “This Book is Gay” by Juno Dawson
10. “Beyond Magenta” by Susan Kuklin

Critics argue banning books questions our sense of democracy and teaches children to shame what they may believe in. And critics said that if a child wants to read a book, they will find a way to do so.

Advocates for book banning said parents should have a decision in what their child reads.

Both ALA and PEN America found common themes among the books called into question. The themes often censored include books involving people of color or the LGBTQ community. The most challenged book for the second year in a row was “Gender Queer” by Maia Kobabe, a memoir about identifying as gender neutral or non-binary.

Sexual content and racism, both, account for just 20 or so percent of the books restricted or banned. And of course some themes overlap. But experts say the spike in book bans comes at a time of “education culture wars” between parents, school officials and educators.

“This is a dangerous time for readers and the public servants who provide access to reading materials. Readers, particularly students, are losing access to critical information, and librarians and teachers are under attack for doing their jobs,” director of the ALA’s Office for Intellectual Freedom Deborah Caldwell-Stone said.

In total, PEN America found that book bans are occurring in 86 school districts across 26 states, which includes 2,899 schools with over two million students enrolled.

In the U.S., Texas has the largest number of districts enacting bans and individual bans.

Conservative attacks against schools and libraries have proliferated nationwide over the past two years, and librarians themselves have been harassed and even driven out of their jobs. A middle school librarian in Denham Springs, Louisiana, has filed a legal complaint against a Facebook page that labeled her a “criminal and a pedophile.” Voters in a western Michigan community, Jamestown Township, backed drastic cuts in the local library over objections to “Gender Queer” and other LGBTQ books.

The executive director of the Virginia Library Association, Lisa R. Varga, says librarians in the state have received threatening emails and have been videotaped on the job, tactics she says that “are not like anything that those who went into this career were expecting to see.” Becky Calzada, library coordinator for the Leander Independent School District in Texas, says she has friends who have left the profession and colleagues who are afraid and “feel threatened.”

“I know some worry about promoting Banned Books Week because they might be accused of trying to advance an agenda,” she says. “There’s a lot of trepidation.”

The Associated Press contributed to this report.