Hundreds of companies are lining up to bid on building President Trump’s controversial border wall.

As of Tuesday evening, 225 companies — mostly construction and engineering firms — have expressed interest in building the wall along the U.S.-Mexico border, according to a website for contractors interested in doing business with the federal government.

The list includes construction companies such as Caddell, engineering firms and top defense contractor Raytheon.

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A number of small businesses have also applied, including 20 owned by Hispanic-Americans who could come under scrutiny for helping to build the controversial wall that critics say represents Trump’s hostility toward the immigrant community.

On the campaign trail, Trump’s proposal to build a wall was a key part of his plan to crack down on illegal immigration.

The United States shares a nearly 2,000-mile border with Mexico, but it is unclear whether a physical wall would span across the entire border.

The Department of Homeland Security estimates it will cost more than $21 billion to construct a wall along the southern border, but critics say the costs could be much higher.

Trump hopes to complete construction of the wall by the end of his first term.

Contractors who have expressed interest in the project have until March 10 to submit a prototype concept paper, followed by a formal request for proposal by March 24.

The Trump administration could hire multiple companies beginning in April.