(CNN) An internal Customs and Border Protection memo obtained by CNN suggests that US border officers working at Canadian ports of entry were directed to detain and question travelers of Iranian descent, including American citizens, in the wake of the killing of a top Iranian general in early January, despite previous denials from the agency.

The single-page undated document, issued by the Tactical Analytical Unit of CBP's Seattle Field Office, is titled "Iranian Supreme Leader Vows Forceful Revenge after US Kills Maj. General Qasem Suleimani in Baghdad -- Threat Alert High."

The memo states that, among others, anyone born in Iran, Lebanon or the Palestinian territories between 1961 and 2001 should be vetted, along with anyone who has connections to those countries and territories. The focus is clearly placed on Iran and some of its potential sympathizers from the region.

CBP officials have previously denied that there was any directive to question people at the border based on ethnicity after dozens of American citizens of Iranian descent said they were stopped at a port of entry in Blaine, Washington, in early January following the general's death. Some were detained for hours and reported that they were asked detailed questions about their country of birth as well as religious affiliations and military service. Others alleged their passports and car keys had been taken by officers during questioning.

A source familiar with the document confirmed its authenticity to CNN.

The memo says to ask travelers questions about connections to the military, particularly Iran's Revolutionary Guard and its elite Quds force and is charged with carrying out and coordinating overseas operations.

"What NTC is looking or is membership in a specialized unit -- QUDS forces: however, this group is so elite and well trained to evade," the memo reads in part. "Anyone can state they are from a different faith to mask their intentions. TAU recommends scrutiny on military questions. We have not yet had anyone admit being in IRGC or QUDS forces yet."

Democratic Rep. Pramila Jayapal of Washington said in a statement that, if verified, this is "absolutely unacceptable, and it reminds us of the dark times in our country's history. We cannot implement loyalty tests or discriminate against individuals in the name of national security."

In a statement, the American Civil Liberties Union said, "if this report is true, CBP has been caught in a lie."

"That scenario is under investigation," Customs and Border Protection Office of Field Operations Executive Director Dan Tanciar said at a press conference in Washington, DC, on Thursday morning. "We would point back to the previous statements that we've had on the issue, but I will say, that we do not, there is no policy, there is no rule that would permit us to target or stop individuals based on one, their nationality alone. We have lots of facts that we have to cover, but that specific incident that you raised is under investigation and I will have to defer any kind of comment on that until that's run its course."

The purported memo also says to ask travelers about extremist ideology or links to terrorism and other criminality. The memo reads in part, "Even if they are not of SHIA faith, anyone can state they are Baha'i, please question further to determine this is the case. When in doubt send for high side check."

It says to vet "Palestinians and Lebanese" who "May have traveled to/from Israel and Jordan." As well as "Iranian and Lebanese Nationals... From Middle East, Africa, and Latin America (includes Iranian/Lebanese nationals with Nexus to Afghanistan, Pakistan, Syria, Jordan, Israel." The memo also states that "Any other nationality that has traveled to Iran or Lebanon" should also be vetted.

Immigration attorney Leonard Saunders, who provided the document to CNN, said it was delivered to his Blaine, Washington, office around noon Wednesday by a man who declined to give his name.

John Cohen, a former counterterrorism coordinator at the Department of Homeland Security, told CNN, "This is certainly the type of document I'd expect to see going out to personnel working at ports of entry during a period of heightened risk." Cohen, now a professor at Georgetown University, added, "During these periods of heightened risk, it's important CBP leadership do two different things, make sure personnel is informed but also ensure that abusive behavior by frontline personnel and violation of constitutional rights won't be tolerated."

Earlier this month, the US government increased scrutiny of travelers and cargo bound for the United States by making a revision to an alert system used to notify officers of those who may need additional screening amid rising tensions with Iran, sources familiar with the change told CNN. The change was part of the administration's increased security posture following the US drone strike in Iraq that killed Soleimani.

At the time, Iranian-Americans said they were detained at the Blaine crossing, over the first weekend of the new year, CBP confirmed there were increased wait times "to an average of two hours on Saturday evening, although some travelers experienced wait times of up to four hours due to increased volume and reduced staff during the holiday season."

But the agency categorically denied there was any directive to stop and question people of Iranian descent. CBP press secretary Matt Leas said in a January 5 statement "social media posts that CBP is detaining Iranian-Americans and refusing their entry into the US because of their country of origin are false. Reports that DHS/CBP has issued a related directive are also false."

Darian Vaziri, a 21-year-old college student from Los Angeles, had been visiting Seattle over the holidays with family when they decided to go to Vancouver for a quick visit. He said they were stopped on the way back into the US.

"They took us into a room," Vaziri told CNN. "We noticed it was only minorities in there. As time went on, we realized it was only Iranians in there." Vaziri says his mother was apparently asked if she had any cult affiliation. "That's what she said. Was she connected to any Shia group. She just said she had no idea what they were talking about."

Shortly after midnight, Vaziri said, "They literally just handed our passports back and said, 'You're free to go.'"

In a message sent to congressional staff this month and obtained by CNN, CBP reiterated that there was no national directive or memo "from DHS or CBP leadership with instructions to detain Iranian-Americans."

Last week, CNN reported on an email sent by an unnamed CBP officer to Saunders in which that officer wrote, "This thing that happened was Seattle Field Office wide." Stating, "Multiple Americans of Persian birth were held and interrogated at length." He said the directive was only lifted January 5, "as soon as it hit the national news."

The officer said he was directly involved in the questioning of Iranian-born travelers. "We asked them standard counter terrorism inspection questions. Was there an Immigration reason for detaining them? No. Was there a Customs reason for detaining them? No. Was the sole reason we detained and questioned them due to their national origin? Yes. Was it the right thing to do? No. Where (sic) their constitutional rights violated? Probably."

At the time that officer did not provide a copy of the directive, or the email he claims was sent lifting the order. The officer also wrote, "I am worried that doing the right thing will get me in trouble."