The experts said the revised order would "jeopardize our relationships with allies and partners on whom we rely for vital counter-terrorism cooperation and information-sharing."
The order temporarily blocks for 90 days citizens from six countries from entering the US unless they are visa holders or are permanent residents of the US. It replaces an earlier order that was held up by a federal court of appeals.
Signers on the letter include former Secretary of States Madeline Albright and John Kerry, and several high-ranking military officials such as retired retired Rear Adm. Donald Guter, The Washington Times reported.
The letter also noted that following the Sept. 11 terrorist attacks, the US created a rigorous vetting system for travelers.
"Since then, the US has added enhanced vetting procedures for travelers and has revised them continuously," the letter said. "Our government applies this process to travelers not once, but multiple times."
The experts said they were heartened that Iraq was removed from the 90-day travel ban, as the country was included in Trump's first executive order. However, the experts added that Iraqis who helped the US military or other services would find trouble with resettlement into the US due to a 120-day suspension of the US Refugee Admissions Program and overall reduction in refugee admissions.
"These individuals were given priority access to US resettlement under the Refugee Crisis in Iraq Act, but their resettlement, like that of many other vetted refugees, will now likely be delayed as security clearance and other approvals expire, adding many more months onto their processing," the letter said.
Going forward, the experts asked that any vetting enhancements be consistent with the US constitution and immediately restart a "strong non-discriminatory refugee resettlement initiative."