Plans for national identity cards could increase the risk of police officers picking on people from ethnic minorities, the race watchdog has said.
ID card plans have proved controversial
Trevor Phillips, chairman of the Commission for Racial Equality, told MPs there needed to be a full study on the race impact of ID cards.
The Commons home affairs committee also heard concerns about using the cards to regulate access to medical treatment.
Fears were also voiced about the effect of the plans on transsexuals.
From 2007 all new passports and driving licences will include biometric data, such as fingerprints or iris scans, and there will be separate identity cards for those who do not drive or have passports.
The Home Office hopes the scheme will be compulsory by 2013.
Last week the information watchdog outlined his "increasing alarm" about the details of the scheme.
The cards will not be compulsory to carry but the CRE is pointing out that black people are eight more times more likely than white people to be subjected to police stop-and-search powers, and Asians three times more likely.
On Tuesday, Mr Phillips said there had yet to be a proper race impact assessment on the plans.
He said ethnic minority groups were uneasy because they believed that some police officers could abuse the system.
There was no evidence that such problems could happen but it would take years to establish whether the problem was real or not, he argued.
Mr Phillips said Muslims might be among those who could feel the cards were another way of picking on a particular community.
"That is really the problem here," he said. "There is a disjunction between what might be true and what people feel to be true.
"Our concern is what people feel might be true could have an impact on community relations."
He suggested one way of countering the problem was for a watchdog to monitor whether ID cards were being checked in different ways for people from different communities.
That could mean that ethnicity was one of the biometric details held on the card, he suggested.
Mr Phillips was also worried that foreign nationals will be the first to have to their own ID cards.
The CRE says the plan could send a message that "suggests that foreigners are second-class people within society".
"This would not promote good relations between different national or ethnic groups," said a paper it gave the committee.
Mr Phillips also warned there would be "chaos and catastrophe" if Britain's 100,000 gypsies and travellers had to keep changing their address details on the cards.
The ID cards could be used as entitlement cards for treatment on the NHS.
Vivienne Nathanson, from the British Medical Association, said she was happy with that concept.
But she was worried there were no hard facts to support claims about the cost of people getting NHS treatment without being entitled to it.
There was a danger the bureaucratic costs to the NHS of checking ID cards could outweigh the cash benefits, she warned.
There also needed to be "sensible" regulations on denying access to people whose did not urgently need treatment but whose conditions, if left unchecked, would eventually lead to much more expensive emergency care.
She cited the example of an asylum seeker who had been denied permission to stay in Britain but was trying to get free insulin for their diabetes.
Claire McNab, from the Press for Change campaign group, said more work was needed to assess the potential impact on the cards on trans-gender people.
DNA matching could be a problem because of trans-gender changes, she suggested, and there could be privacy issues over verification of the cards.