As investigators look for clues and suspects in the nation's worst terrorist attacks, some legal experts worry they might stop people for questioning simply because they look Arab or Muslim.
"I'm very worried about what's going to be done in the name of security," Kevin Johnson, a racial profiling and immigration expert at the University of California at Davis Law School, said.
Mr Johnson said he expects "blunt stereotyping and shaking down" of people who appear Middle Eastern even though "it's blatantly illegal".
About a dozen travellers of Middle Eastern descent were detained at two New York airports on Thursday, only to be cleared later of any connection with this week's terrorist attacks.
It is illegal for law officers to target someone based on ethnic appearance. Courts have also historically ensured that foreign nationals are guaranteed the same civil rights as US citizens.
Nevertheless, officers are under intense pressure to track down potential conspirators and "they can decide to heck with the due process rights of these people, we might be on to something," said Ms Christine DeConcini, director of advocacy for the Washington-based Catholic Legal Immigration Network.
"I'm all in favour of getting leads, but people's civil liberties and civil rights need to be protected. I don't want to hear that they're ransacking house after house," she said.
The US Justice Department said a number of people questioned in connection with the plot have been arrested for immigration violations and were in the custody of the Immigration and Naturalization Service.
Arab-Americans, Muslim and others groups have reported harassment and violence since the attacks on the World Trade Centre and Pentagon. Most of that has come from other Americans.
President George W. Bush said on Thursday that "we must be mindful we treat Arab-Americans and Muslims with the respect they deserve."
Mr Kareem Shora, legal adviser to the Arab American Anti-Discrimination Committee in Washington, said the group has not received reports of rights violations by law agencies.
"Mistakes will be made. You can't have a perfect investigation. As far as we know, no intentional mistakes are being made," Mr Shora said. "Everybody understands it's a very special situation. We all have to cope with it."
After the Oklahoma City bombing, innocent people found themselves targeted because they fitted a government profile, said Michael Scaperlanda, a University of Oklahoma law professor.
"In a time of heightened security, there's always a danger that law officers will go overboard and overreach in their quest to keep us safe," said Mr Scaperlanda. "Police officers generally can find some reason to stop somebody. It is going to take sensitive balancing."
AP