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On Tuesday, the House of Representatives voted to curtail the Visa Waiver Program, which enables tourists from 38 countries to travel to the U.S. for up to 90 days without first applying for a visa, Mashable reported. The bill would require travelers from these waiver countries to undergo the visa process if they’ve visited Iraq, Ira, Syria and Sudan.–Fortune Editors

By Nikki Ekstein, Travel & Leisure

On Monday, Donald Trump called for a total ban on Muslim travelers to the U.S. But perhaps the billionaire—who partially makes his keep off the travel industry—hasn’t considered the economic impact of his proposed policy. Banning Muslim travel isn’t just a betrayal of American ideals, it’s also a costly proposition. Currently, there’s no way to track tourists by their religion, but here’s a back-of-the-envelope look at what it would really mean to cut Muslim travel from the U.S. economy.

According to a 2012 study cited in the business publication Economy Watch, the six countries of Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, and the UAE represent a majority of the Middle East’s travel spending, and account for 37 percent of all Muslim travelers worldwide. With that in mind, we looked at the spending habits of Middle Eastern travelers to the U.S. as a way to gauge the impact of Muslim travel at large.

In 2013, just over one million Middle East-based travelers passed through U.S. customs, according to the U.S. Travel Association. That year, these travelers spent an average of $6,000 each for a total of $6.8 billion. (European visitors, by contrast, spend less than $4,000 on average when they visit the U.S.)

Of course, the Middle East also includes the mostly non-Muslim country of Israel. However, Israel’s 8 million residents make up a mere 0.1 percent of the total population in the Middle East; it’s a negligible contributor to the region’s $6.8 billion sum.

Still, travelers from the Middle East represent just over 37 percent of Muslim travelers overall; the region excludes Turkey, Indonesia, and Malaysia, among others, which are also predominantly Muslim.

Multiply this $6.8 billion figure to represent the full scope of Muslim travelers arriving in the U.S., and the total cost of Donald Trump’s ban could be as high as $18.4 billion. What’s more, that figure is the cost estimate before you factor in what it would cost to overhaul the country’s screening systems.

*All facts and figures represent the most current data available, and are sourced from the U.S. Travel Association, unless otherwise noted.

This article was originally published on TravelandLeisure.com.