People from certain ethnic groups are more likely to be stopped and searched on London transport in the wake of the bombings, British Transport Police say.
Hazel Blears says "decent people" will accept the move
A force spokesman said communities were not being singled out, but police have to "target the people we think may be involved" in bomb attacks.
The policy has been supported by Home Office minister Hazel Blears.
But Civil rights group Liberty said the move would lead to bombers using people who did not fit the usual profile.
Ms Blears said officers would be acting on descriptions from intelligence sources.
She told BBC News: "That's absolutely the right thing for the police to do.
"What it means is if your intelligence in a particular area tells you that you're looking for somebody of a particular description, perhaps with particular clothing on, then clearly you're going to exercise that power in that way."
She said it was important people were kept informed and those who were stopped were given an explanation.
"I think most ordinary decent people will entirely accept that in terms of their own safety and security," she added.
But Shami Chakrabarti, chief executive if Liberty, believes the move plays into the hands of bombers.
She said: "If you search people of a particular race or description while letting others through, it doesn't take long for a terrorist group to learn ways of placing their lethal cargo with those who don't meet the profile."
The transport police spokesman said: "We are not singling out a community - we are after criminals within all communities, so it isn't singling out a community.
"Clearly if we are looking for people and being operationally efficient, we have got to target the people who we think are maybe involved.
"It is going to be disproportionate. It is going to be young men, not exclusively, but it may be disproportionate when it comes to ethnic groups.
"We are very sensitive to the effects that that can have and it isn't an attack on particular communities."