A new state law in Arkansas that could send librarians and booksellers to prison was challenged on Friday in a federal lawsuit filed by libraries, independent bookstores and publishers who said the legislation was unconstitutional.

The suit comes as states and counties around the country are increasingly restricting the availability of certain kinds of books, and as those who oppose such regulations are finding more ways to push back.

The complaint, which was filed in the United States District Court for the western District of Arkansas, said the law “forces bookstores and libraries to self-censor in a way that is antithetical to their core purposes.”

The Arkansas law, which is scheduled to go into effect in August, requires any material that might be “harmful” to minors, including books, magazines and movies, to be shelved in a separate, “adults only” area.

Adam Webb, the executive director of the Garland County Library in Hot Springs, Ark., said on Friday that the law puts librarians in an impossible situation.

“They’ve created this catch-22,” said Webb, who is among the plaintiffs. “Either I comply with the law but violate the constitutional rights of my patrons, or I uphold the constitutional rights of my patrons and possibly get charged with a crime.”

The lawsuit said that many libraries and bookstores don’t have room for such a space, and that a separate area would stigmatize the materials and make it more difficult for adults with children in tow to access them. The law also creates a process for challenging materials that, according to the complaint, favors those who want books removed.

Crucially, the law also ends a protection for librarians and educators that shields them from prosecution if they use educational materials or provide books that some might find objectionable. It also makes it a misdemeanor, punishable by up to a year in prison, for librarians and booksellers to distribute a “harmful item” to a minor.

“This is a case that has broad implications for not only the ability of people to access materials in libraries in Arkansas, but for overall foundational principals of our democracy,” said Skye Perryman, the chief executive of Democracy Forward, which is representing the Arkansas Library Association in the lawsuit. “If this law were to go into effect, librarians could face jail time for failing to take actions that flagrantly violate the U.S. Constitution and Arkansas Constitution.”

Allison Hill, the chief executive of the American Booksellers Association, a trade organization for independent bookstores that also joined the suit, said the new law could have a chilling effect and lead to a “a Wild West where anyone can object to any book and a bookseller could end up with a felony record.”

State Senator Dan Sullivan, who sponsored the bill, defended the law in an opinion piece in The Arkansas Democrat-Gazette in May.

“We don’t exempt pharmacists from drug-dealing laws, slaughterhouses from animal-cruelty laws and doctors from sexual-assault laws,” he wrote. “Yet prior to my bill, teachers and librarians, who are the closest to our children, were 100 percent legally free to provide children obscene material at their jobs.”

The lawsuit is the latest sign that organized opposition is building among those who are against book bans. According to the American Library Association, there were more efforts to remove books from libraries in 2022 than ever recorded, and nearly twice as many as in the previous year.

An April report from the free speech organization PEN America found 4,000 instances of book removals since the group began tracking them in July 2021. The majority of challenged books feature L.G.B.T.Q. themes and characters, or address race and racism.

Both organizations attributed the spike to the growing influence of conservative organizations like Moms for Liberty and Utah Parents United, which have lobbied for book removals at school board meetings and on social media. They also cited the growing number of state laws that limit the kinds of books that can be available in libraries and schools, and in some cases make librarians and teachers vulnerable to criminal prosecution.

But free speech organizations, publishers, library groups and residents are aiming to counter book bans with lawsuits, and laws, of their own.

Last week, a group of parents in Crawford, Ark., sued over the county’s policy of removing books with L.G.B.T.Q. themes from the children’s section of libraries and placing them in a separate “social” section.

In Illinois, the legislature recently passed a bill, which Gov. J.B. Pritzker is expected to sign, that would prohibit libraries from removing books and withhold funding from libraries that decline to adopt a policy against book banning.

PEN America and the country’s largest publisher, Penguin Random House, recently filed a lawsuit against the Escambia County school district in Florida, arguing that the district had violated students’ First Amendment Rights by limiting their access to books on certain subjects.

On Friday, the Association of American Publishers and six publishing companies filed a brief in support of a group of residents in Llano, Texas, who sued the county and library officials over book removals, arguing that the bans were unconstitutional and violated citizens’ First Amendment rights.

“Any suppression of viewpoints or content is dangerous to publishing,” said Maria Pallante, the president and chief executive of the Association of American Publishers, which has also joined the lawsuit challenging the law in Arkansas. “It’s OK to have strong opinions about a book, but not OK to restrict access for other people through the weight of the state.”