A draft executive order obtained by the Huffington Post outlines President Donald Trump's plans to ban refugees and restrict immigration from seven predominantly Muslim countries.

The draft, which could be amended before Trump signs it, also calls for suspending the "visa interview waiver program" and ensuring "compliance with section 222 of the INA [Immigration and Nationality Act], which requires that all individuals seeking a nonimmigrant visa undergo an in-person interview, subject to specific statutory exceptions."

Here's what to know about the visa waiver program.

Here's what to know about the visa waiver program. Scott Olson/Getty Images

What does the visa waiver program do?

According to the Department of State, the visa waiver program grants citizens of 38 countries a 90-day tourist visa to the United States after submitting their biographical information to a screening check. Citizens from the waiver program's participating countries who also happen to be nationals of Iraq, Iran, Syria or Sudan are not eligible to travel to the United States.

Travel purposes permitted under the visa waiver program include contract negotiations, short-term trainings, conference attendance and business-related matters. Travelers are also allowed to enroll in short recreational courses of study; participate as amateurs in entertainment, sports events or contests unless being paid for participating; receive medical treatment; visit with family; and engage in tourism.

Activities not allowed under the visa waiver program include studying for credit, undertaking employment, working as a foreign press or taking up permanent residence in the United States.

What will change if Trump suspends the program?

Thirty-eight countries participate in the waiver program, including most European countries, Australia, Japan, Chile and Taiwan. If Trump eliminates the program, people from those countries seeking a nonimmigrant visa will be required to "undergo an in-person interview, subject to specific statutory exceptions," according to the draft of the executive order.

According to section 222 of the INA, citizens of other countries between the ages of 14 and 79 and applying for nonimmigrant visas must already undergo an in-person interview with a consular officer, unless the requirement is waived.

The visa waiver program has evolved over time

If the draft executive order goes into effect as is, it won't be the first time the visa waiver program has experienced modifications.

In December 2015, former President Barack Obama strengthened the visa waiver program by modifying the Department of Homeland Security's Electronic System of Travel Authorization, which collects information from U.S. law enforcement and intelligence agencies to determine whether a traveler poses a serious security threat.

According to a statement from the White House at the time, the waiver program allowed INTERPOL to track lost and stolen travel documents while sharing information with European partners. The announcement occurred in the wake of the Paris attacks that killed at least 130 people.