NEW YORK -- A former senior lawyer for the National Security Agency has called plans to force visitors to the US to turn over contacts lists, browsing histories, and social media data "tremendously intrusive" and "grossly overbroad."

April Doss, former associate general counsel for intelligence law at the National Security Agency, argued in a phone call that such a move would almost certainly be unlawful.

A second former NSA lawyer, Susan Hennessey, appeared to concur. In a tweet, she said that "when April said something violated the law, that was the end of discussion."

CNN reported Sunday that White House policy director Stephen Miller said Trump administration officials are "discussing the possibility of asking foreign visitors to disclose all websites and social media sites they visit, and to share the contacts in their cell phones."

Miller added that foreign visitors who decline to share that information could be denied entry, but sources said that the idea was at a preliminary discussion level.

"It defies belief to my way of thinking that web browsing histories and contacts list of every person who wants to enter the US on a visit could possibly have intelligence value," said Doss.

"Grossly overbroad"

News of the discussions comes two days after President Trump signed a new executive order barring citizens of seven predominantly Muslim nations entry into the US, which sparked protests around the country during the weekend and widespread condemnation from major tech companies whose employees were also affected by the order.

After the ACLU brought forward a case, a federal court stayed the executive order, preventing any deportations for the time being.

The former NSA lawyer, whose job provided legal advice on the NSA's intelligence operations as well as ensuring compliance with privacy and civil liberties policies, explained that the government neither has the capacity to conduct deep-dive searches on every visitor at the border, nor has the legal powers to do it once they are permitted entry to the US.

Doss said that it would be "tremendously intrusive" if US border officials were searching the contents of communications, such as contacts lists and social media information, which people are generally afforded a reasonable expectation of privacy.

Even with browsing data, she said that it's "pretty well established in US law" that web searches and news articles can be construed as content if the name of the article is in the web address, for example.

"To ask every single visitor to the US to provide this information would certainly be grossly overbroad," she said.

International fallout

Rules like this, if enacted, could have serious domestic and foreign policy implications for the Trump administration.

Doss warned that the international ramifications may diminish intelligence sharing between the US and other countries, such as Iran which has reportedly already banned US citizens from entering the country.

International trade and data flows could be interrupted, she said.

I can't imagine [Privacy Shield] surviving something like this," she said, "because it would be very hard for European data protection authorities to reach a level of comfort with this kind of personal data from individuals simply as a requirement of traveling into the US."

"This could precipitate or [be] used to further propaganda for adversaries of the US," she added.

Already, social and media channels belonging to so-called Islamic State are said to be "taking advantage of the situation" by sharing articles by Western media outlets instead of their own propaganda.

"Detrimental to intelligence activities"

Doss, who served for more than a decade at the intelligence agency, warned that there could be a negative impact on effective intelligence gathering, if such a plan was implemented.

"There is no conceivable fashion in which all of the information from every person who wishes to enter the US on a visit has anything to do with national security or lawfully authorized intelligence gathering activities," she said.

"To do that sort of collection on this scale would be quite detrimental to intelligence activities because you would get so much garbage that has nothing to do with anything," she added.

She said that the move would be a "tremendous drain on resources" because the volume of people coming in would make finding a needle in a haystack "several hundred million times larger."

That could hamper and distract intelligence officials "from doing much more focused work that could have very important outcomes," she added.

"That could be a real cost to effective intelligence gathering," she said.

A spokesperson for the White House did not return an email requesting comment.