Federal authorities have detained an Iranian woman in an Oregon jail even though she has a tourist visa to visit her family in the US, according to the American Civil Liberties Union.

The detention of Alia Ghandi at the Portland airport has renewed fears that agents with US Customs and Border Protection (CBP) are targeting travelers from Muslim-majority countries despite the fact that federal courts have repeatedly blocked Donald Trump’s controversial travel ban.

Ghandi, 29, was detained for several hours after she landed in Portland on Tuesday and was eventually transferred to a county jail 80 miles away, according to Mat dos Santos, legal director of the ACLU of Oregon.

“That is a terrifying circumstance,” Dos Santos said in an interview on Wednesday. “That is something that anybody would think is just a completely unacceptable way to treat anyone, especially somebody here on a valid visa and not to our knowledge being accused of having committed any kind of crime.”

It is unclear why CBP is blocking her entry. A spokesperson said the detention was not related to Trump’s recent executive order seeking to restrict travel from six Muslim-majority countries, including Iran.

Ghandi is an architect who lives with her parents in Iran and was planning to visit her sister, who lives in Portland and is a US citizen, according to the ACLU. Ghandi was briefly able to talk to her sister by phone after she arrived, but since then has been unable to communicate with relatives or attorneys, Dos Santos said.

“Imagine arriving in a foreign country, being held for hours at an airport for reasons you don’t understand, then being transported to a jail an hour and a half away and denied the ability to talk to your local family.”

Trump’s travel ban, signed on 6 March, aimed to block entry to the US for 90 days for citizens of six Muslim-majority countries and was a revised version of an order Trump released in January. The original order sparked chaos in airports across the country and was suspended by a judge.

The reworked ban sought to address the legal challenges and removed Iraq from the list. But opponents, including the ACLU and numerous state officials, have successfully argued in court that the order continues to constitute religious discrimination. At this time, the ban remains halted, leaving many immigrants in a legal limbo.

CBP declined to comment on the specifics of Ghandi’s case, but said in a statement that “having a ‘valid visa’ does not guarantee a foreign national entry into the US”, adding, “A traveler regardless of their country of nationality can be found inadmissible into the US for various reasons.”

Dos Santos said it was unusual and troubling that Ghandi was forced to spend the night in a jail. The customs spokesperson claimed that the Portland international airport does not have a CBP holding facility for an overnight stay and that it is “customary” to transfer a traveler to a local jail.

Bryan Brandenburg, administrator at the Northern Oregon regional correctional facility, a county jail, said Ghandi was held for about 12 hours at the facility from 5pm to 5am and has since returned to Portland. He claimed that the jail does not hold people simply based on their immigration status and that Ghandi was at the facility due to a “federal warrant”, though he said he could not provide further details.

Dos Santos, however, said the ACLU has received no indication that there are any criminal charges or investigation. The CBP spokesperson also said Ghandi was not facing a criminal charge and described her case as a “minor administrative violation”.

Dos Santos said it was difficult to know whether the detention was an isolated decision from local CBP officials “or something coming down from headquarters”. The ACLU in Oregon has been involved in numerous high-profile cases involving detained immigrants.

“This has just been incredibly painful and confusing,” added Dos Santos, who has been in contact with Ghandi’s relatives. “This is a family who by all accounts was just looking forward to a nice vacation.”