President Donald Trump announced a sweeping immigration proposal Thursday that would alter the way legal immigrants are allowed into the U.S. The plan includes a civics test, a measure that experts said was highly unusual and could exclude high-skilled applicants from entering the country.

“This test is at best unnecessary and could screen out some very skilled, ambitious immigrants who are ready to be productive in America, whatever the test says,” said Daniel Griswold, senior research fellow at the Mercatus Center at George Mason University and co-director of its Trade and Immigration Project.

“It could be a barrier to very productive immigrants becoming a part of American society,” he said.

Griswold and others said that while the details of Trump’s proposal remain unclear, they have never heard of such a requirement at that level in the immigration process. Such exams are usually part of citizenship tests, they said.

“It’s like asking for people to apply for citizenship when they arrive,” said Theresa Brown, director of immigration and cross-border policy at the Bipartisan Policy Center, a Washington-based think tank. “It’s a big thing to ask of people from other parts of the world.”

Trump’s proposal would create a system that favors applicants who are highly skilled, well-educated and speak English, as well as have potential employment over family-based immigration.

The White House estimates 12 percent of people who obtain green cards and citizenship do so based on “employment and skill,” while 66 percent enter via family-based connections and 22 percent through humanitarian visas and the diversity lottery. Under the new proposal, employment and skill would increase to 57 percent, 33 percent for family-based and 10 percent for everything else.

The merit-based system proposal is centered around what would be called the "Build America" visa. It recognizes three categories: extraordinary talent, professional and specialized vocations, and exceptional students.

The U.S. grants about 1.1 million green cards a year, including to people already living in the U.S. on visas. The administration has said the number would not change, just the composition.

But Brown said that would depend on what the points system would look like.

“How many people would meet the new point criteria and how many of those want to come to the U.S.?” she said. “They may or may not be able to keep the numbers the same."

The Trump administration has repeatedly touted so-called merit-based or points-based systems, such as in Canada and Australia.

Immigration and economic experts said those countries also bring in many refugees and give value to immigrants with family already in those countries.

While the U.S. has historically resettled more refugees than the rest of the world, that number has steadily declined under the Trump administration. Meanwhile, Canada and Australia have been leading in the number of refugees admitted per capita.

Griswold said through his research he has compared the U.S., Canadian and Australian systems and found “the big differences are Canada and Australia admit significantly more people relative to the population.”

“They’re more generous in admitting immigrants as part of their population,” he said.

He added his main concern with Trump's proposal was that it would “cut deeply into family-based migration.”

Family-based migration was already bringing in educated, highly skilled people, he said.

“In fact, the current inflow of family-based and diversity lottery immigrants are better educated than the average American,” he said.

“It’s a myth that you either let in high-skilled immigrants or we get low-skilled, poorly educated family-based immigrants,” he said.

Brown added that the Canadian system awards points to immigrants for having family ties in the country.

“They admit more family relatives than the United States on a per capita basis,” she said.

Such points-based systems come with their own set of problems, Griswold said.

“Canada and Australia have found it can create a mismatch between the workers who are approved and what industry really needs,” Griswold said. “It’s a top-down system where the government decides what kind of workers we need.”

He added that while adding more high-skilled workers was valuable to the American economy, “let them be the workers U.S. industry needs right now to be more productive.”

Kate Hooper, a policy analyst at the nonpartisan Migration Policy Institute, said it was also “worth highlighting that Australia and Canada have parliamentary systems” of government, unlike the U.S. That could make it even more difficult for the U.S. to update its system based on economic needs.

“The question really is how the U.S. system would be designed so you could regularly update the system in the same way,” she said.

Trump’s plan does not address the status of immigrants brought to the U.S. illegally as children and thus is a nonstarter with Democrats in Congress, but on Thursday Trump said if his plan was not adopted “for political reasons,” he would work to get it passed after the 2020 election if Republicans win back control of the House of Representatives.