CEOs of some of the country's biggest companies are warning that President Donald Trump's immigration policies pose a threat to the economy and hurt American competitiveness.

The executives are part of the Business Roundtable, a pro-business organization, and include some of the best-known corporate leaders in the U.S., such as Jamie Dimon of JPMorgan Chase, Tim Cook of Apple and Ginni Rometty of IBM. In their letter to Kirstjen Nielsen, the secretary of Homeland Security, the executives outlined their concerns with what they decry as "arbitrary and inconsistent" immigration policies.

"Inconsistent government action and uncertainty undermines economic growth and American competitiveness and creates anxiety for employees who follow the law," the executives wrote in the letter, which was delivered on Wednesday. "In many cases, these employees studied here and received degrees from U.S. universities, often in critical STEM fields."

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The unusual step highlights the tension between the Trump administration's immigration policies and the needs of American corporations, which have long relied on workers from around the world to fill positions. The letter comes as Republican leaders, including President Trump, are condemning illegal immigrants after a Mexican laborer was arrested in the murder of Iowa college student Mollie Tibbetts.

The executives stressed that legal immigrant workers are facing increased uncertainty over their immigration status and may be forced to leave, even though the Department of Labor has, "in many cases, certified that no qualified U.S. workers are available to do that person's job."

The group added that the Trump administration's policies are also discouraging would-be workers from other countries from considering taking jobs in the U.S.

"The reality is that few will move their family and settle in a new country if, at any time and without notice, the government can force their immediate departure -- often without explanation," they wrote.

Other issues the CEO group highlighted include the revoked status for spouses of legal immigrants; inconsistent immigration decisions; confusion about what type of information is required for visa applications; and the use of immediate deportation proceedings if an application is denied.

Wrote the CEOs: "Our employees are concerned that they will face removal proceedings even if they have complied with immigration laws and intend to promptly depart the country."