US Customs and Border Protection has denied racial profiling, after a Pakistan-born New South Wales MP said she was interrogated about how she got an Australian passport as she entered the US.

Greens MP Mehreen Faruqi, who was born in Pakistan, has criticised immigration procedures at Los Angeles International Airport, saying she and her husband were asked "how we actually got our Australian passport" before being interviewed in separate rooms.

"Questions about why I was there, when I had last been to Pakistan, what I had done there, had I been to the US before," she said, adding she was also asked to provide a second form of identity, and underwent routine fingerprinting.

She said the process pointed towards racial profiling, but US Customs and Border Protection denied the claim.

The agency has told the ABC that as part of its "critical national security mission", officers check the validity of travel documents on all travellers "regardless of nationality, race, sex, religion, faith, or spiritual beliefs".

"We do this routinely every day," a spokesperson said in a statement.

"It's not unusual that a legitimate traveller may be subject to an enhanced screening. This protects not only the traveller but ensures the integrity of our border security mission.

"To put this in perspective, CBP intercepts an average of 27,000 illegitimate documents every year.

"CBP welcomes more than a million passengers arriving to the United States every 24 hours. Every day CBP officers conduct their duties with vigilance, integrity and the highest level of professionalism."

Dr Faruqi migrated from Pakistan to Australia in 1992 with her young family and joined the Australian Greens in 2004.

She is touring the United States as part of a self-funded fact-finding trip on drug law reform and also to visit family.