Human rights activists are expressing concern that a new State Department directive requiring consular officials to look through social media accounts of some visa applicants will effectively expand President Trump’s Muslim ban — and be used to exclude people with certain political viewpoints.

On Thursday, Reuters reported that even as some key parts of Trump’s Muslim ban executive order are being held up by legal challenges, Secretary of State Rex Tillerson has ordered “mandatory social media checks” on visa applicants who have ever spent time in territory controlled by ISIS. He also directed embassies and diplomatic missions to identify other “populations warranting increased scrutiny,” whose visas would receive increased scrutiny.

Amnesty International sent a letter to the State Department, requesting that the memoranda and instructions related to the new measures be made public. “These implementation memos should be disclosed because they are a matter of public concern,” the letter reads. “Thousands of people apply for visas to travel to the United States — for urgently needed medical care, to escape persecution, to reunite with their families.”

Naureen Shah, a director at Amnesty International, told The Intercept that if the directive is applied with limited oversight, it could even further broaden Trump’s Muslim ban.

“This is a plan to go beyond the letter of the executive order in ways that the public doesn’t have notice of, and Congress doesn’t either,” she said.

“I read these in the context of an executive order that is premised on the notion that people are presumptively dangerous based on who they are — not on what they’ve done,” said Shah. “I’m not saying that the officials are going to act on that, but that’s implicit here in what’s coming from the State Department at the highest level.”

Shah also expressed concern that the social media vetting will allow the State Department to bar admission to people because they have expressed certain political viewpoints. “The first thing that occurred to me when I read the Reuters story was that this could enable the Trump administration to block people from entering the country who had been on the ground in Iraq and Syria, people like our researchers.”

“There are people who have done this work, who have travelled in ISIS-controlled territory, that come into the United States because they have something to say. They have information to provide. It puts such huge amounts of discretion in the hands of these officials based on the presumption that people are dangerous because they’ve been there. We’re really worried about the ways that could be used.”

The U.S. has a long history of banning entry to people based on ideology. At the height of McCarthyism, Congress passed a law allowing the State Department to ban anyone who acted “prejudicial to the public interest.” The law was promptly used to bar entry to leftist novels, poets, writers, and activists. The government even used the law to block Pierre Trudeau — who would go on to become the Canadian prime minister decades later.

Similarly, the Patriot Act — passed in the wake of the 9/11 terror attacks — allows the State Department to ban anyone who it determines “undermines the United States efforts to reduce or eliminate terrorist activities.” Under Presidents Bush and Obama, that led to blocking of visas for anti-apartheid academic Adam Habib, Greek economist John Milios, and hip-hop artist M.I.A.

The Bush administration in 2004 denied entry to Tariq Ramadan — an internationally renowned professor of Islamic studies and Iraq War critic. The ACLU filed suit on his behalf and won, after the government failed to show a connect to terrorism. But the court, not ruling on whether the law is unconstitutional, did not strike down the law.