President Donald Trump is calling for a "merit-based immigration" system following the deadly truck rampage through a New York City bike path.

The Uzbekistan native Sayfullo Saipov, 29, arrested Tuesday after the attack, entered the United States in 2010 under the Diversity Immigrant Visa Program, which encourages immigration from underrepresented nations. Up to 50,000 visas a year are issued under the program using a lottery system. Trump ripped the program on Twitter Wednesday, calling for an end to the system:

President Trump called for the adoption of a merit-based immigration system in February during his first address to Congress, praising Canada and Australia for using the point-based system.

Here's how the merit-based immigration system works:

Merit-based systems prioritize access to immigrants based on education, specialized skill sets, employment experience, language proficiency and age, according to the Bipartisan Policy Center.

The merit-based system would significantly shift U.S. immigration policy, which currently heavily operates on a family-based system, stemming from unifying members of a family regardless of their economic or educational background. In 2015, 65 percent of those granted lawful residencies petitioned for family-sponsored visas as opposed to the 14 percent of new immigrants admitted through employment or skills, according to the Bipartisan Policy Center.

Immigrants can also be granted legal entry into the country through a U.S. employer, for humanitarian reasons or based on the lottery system.

The system proposed by President Trump would change the proportions of who is let into the U.S. and who is denied entry. The notion behind a merit-based system is that immigrants would contribute to the economy and society. It's backed by the idea that many immigration slots are going to individuals who don't have as much to offer to the U.S. as the country does to them.

Although slightly different, the merit-based immigration system used in both Canada and Australia are based on the number of points granted through selection factors, such as language proficiency, being of prime employment age or a job offer. In Canada, an individual's points can add up to a maximum of 100. In Australia, a person must earn at least 60 points to qualify.

Who would benefit from a merit-based immigration system?

Admitting highly-skilled, educated immigrants would benefit places like Silicon Valley, which seek out only the best and brightest employees. Many leaders in Silicon Valley have long stood against limits on employment-based immigration, as it hurts their ability to recruit talent from all over the world.

The STEM industry would likely greatly benefit from having a diverse pool of talented workers to choose from. Selection factors behind the merit-based system push for assimilation for an easier transition into the professional workforce.

In theory, by having more higher-skilled workers, the country could save money and raise wages.

What are the challenges of using a merit-based immigration system?

Lower-skilled workers make a large portion of the hospitality, health care and food services. Increasing merit-based visas and cutting down on family-based and other visas, could largely disrupt the labor market in these sectors, according to USA Today.

Because such a high number of immigrants entering the country are low-skilled workers, the merit-based system would pose more restrictions on who enters the country overall. The system would naturally keep many people out based on the standards placed on visa grants and therefore reduce immigration.

There is evidence that immigrants who enter countries, such as Canada and Australia, through merit-based immigration face issues with underemployment and unemployment, according to the Bipartisan Policy Center.

This is because many highly-skilled immigrants spend time upgrading their credentials in a new country and don't necessarily have to have a job offer before immigrating to the U.S.

Additionally, many of the traits required by the point system encourage assimilation, which in turn harm the diversity the U.S. prides itself on.

Even if a merit-based system was adopted by the U.S., there will be other visas available for immigrants.

There is no country that operates solely on a merit-based system. Countries such as Canada still grants visas for humanitarian or family reasons. The U.S. already approves temporary visas for workers, students, visitors and family members of legal residents.

Immigrants on temporary work visas, such as H1Bs and H-2As, are still influencing the economy. An H1B visa-- which allows U.S. employers to hire college-graduate, highly-skilled workers-- is the closest program to a merit-based system currently used in the U.S.