Hillary Clinton’s proposal to get money out of politics could allow the federal government to restrict or ban the publication of a book that has embroiled her presidential campaign in controversy, experts say.

Clinton called for a constitutional amendment to "get unaccountable money out of" politics in an op-ed for the Des Moines Register published Monday. Her campaign did not respond to requests for additional details, but legal experts say similar efforts over the past two years would have profound effects on Americans’ free speech rights.

Constitutional amendments introduced by Democratic senators in 2013 and 2014 could give the federal government the authority to prevent expenditures by a publisher, for example, to produce or publicize books critical of political candidates.

One such book, Clinton Cash by Hoover Institution fellow Peter Schweizer, has roiled Clinton’s campaign over the past two weeks. Schweizer suggests in the book that Clinton’s State Department took actions that benefitted donors to the Clinton Foundation.

Under two recently proposed constitutional amendments designed to limit political spending, "You could be prohibited" from publishing a book critical of a political candidate, "or restricted—you can only spend $1,000 in publishing your book or something along those lines," according to UCLA law professor Eugene Volokh.

Though Clinton has not outlined specific language of a constitutional amendment, Volokh called it "telling that some of the most prominent proposals introduced by people who are, after all, senators, would, whether intentionally or not, allow very broad kinds of restrictions" on political speech.

One of those amendments was introduced in 2013 by Sen. Jon Tester (D., Mont.). The measure would have eliminated all constitutional rights for corporations, which include not just traditional for-profit entities but also newspapers, book publishers, film studios, churches, and nonprofit groups.

"The Tester amendment would essentially allow any regulation of any kind of speech by any kind of corporation," Volokh explained. "So if the government wanted to say, ‘corporations can’t speak out about candidates or can’t express unpatriotic views about candidates or can’t express allegedly racist or sexist views about candidates,’ that would be allowed under this amendment."

The amendment, like similar measures, was billed as a response to the Supreme Court’s 2010 decision in Citizens United v. Federal Election Commission. That decision, which liberalized regulations on corporate political speech, came after the federal government tried to prevent the distribution of a documentary about Hillary Clinton produced by the conservative nonprofit group Citizens United.

Like Schweizer’s book, the film, titled Hillary: The Movie, did not ask its audience to vote against Clinton or for her primary opponents. But it was highly critical of the then-New York senator.

Federal law at the time prohibited nonprofits from releasing "electioneering communications" mentioning a candidate for federal office within 30 days of a primary or 60 days of a general election.

Under pre-Citizens United campaign finance law, Clinton Cash would likely have fallen under the same restrictions.

"This is just another attempt by the Clintons and the left to ban opposing voices," Citizens United president David Bossie said in an emailed statement. "Let’s not forget, the federal government claimed they could ban books as they sought to restrict Citizens United’s free speech rights as we tried to promote Hillary: The Movie."

Prior to the court’s 2010 decision, the FEC provided "a safe harbor for communications that … do not take a position on any candidate’s or officeholder’s character, qualifications, or fitness for office," according to a 2008 memo from Washington law firm Holland & Knight.

As ABC anchor George Stephanopoulos noted in a segment on Schweizer’s book, he "raises serious and alarming questions about judgment of possible indebtedness to an array of foreign interests and ultimately, a fitness for high public office."

Before the court’s decision in Citizens United, the federal government could not ban books outright, noted Justice Stephen Breyer, who dissented from the court’s 2010 decision. "What you do is put limitations on the payment for them," he said.

The relevant limitations at the time had to do with the window before an election in which electioneering communications took place. But the two amendments offered in 2013 and 2014 would go much further: Tester’s would remove all First Amendment protections for speech by corporations and nonprofit organizations that criticize a candidate.

The other proposal, authored by Sen. Tom Udall (D., N.M.), would give Congress and state governments the authority to prohibit "corporations or other artificial entities created by law … from spending money to influence elections."

Both proposals would give the federal government sufficient power to restrict or ban outright the publication of Clinton Cash and any other book published by a corporate entity that reflected poorly on a political candidate, according to Volokh.

Even if a book doesn’t explicitly urge readers to vote for or against a candidate, it could still be interpreted as affecting an election if it criticizes or praises a candidate, Volokh explained.

"My book is about candidate X, I think candidate X is a horrible person, and I don’t want to see him elected and that’s why I’m writing my book," he said hypothetically. "Well, that’s spending money to influence elections. You could be prohibited from doing that."

The purpose of campaign finance laws is "the prevention of corruption and the appearance of corruption," according to the Supreme Court. However, while both the Tester and Udall amendments would limit political speech, they would not address other avenues for corruption or the appearance thereof.

The precise activities detailed in Clinton Cash, for instance, would not be addressed by an anti-Citizens United constitutional amendment even though 63 percent of likely voters think foreign government donations to the foundation affected Clinton’s activities as secretary of state, according to a poll released on Wednesday.

"Any proposed campaign finance restrictions aimed at preventing one possible kind of indirect corruption, indirect bribery let’s say, and it doesn’t cover all of them like foreign donations, or for that matter domestic donations, to the Clinton Foundation," Volokh said.

He added that "it would be impossible to take care of all" possible avenues for corruption through federal legislation, but noted that Clinton’s proposal would not address any apparent quid pro quo at her 501(c)(3) charity.

That fact drew charges of hypocrisy from Clinton critics.

"Even if [Clinton] believed in such an Amendment—and decades of their political-financial history shows it as little more than a cheap line tossed out to their gullible throngs—it would do nothing and would have done nothing to stop the flow of influence peddling gifts from hostile foreign governments through their foundation," said campaign finance attorney Dan Backer, who helps run the anti-Clinton Stop Hillary PAC.