Relatives of those who died in the 7 July bombings fear the inquests into their deaths could be heard in secret.
Laura Webb died in the explosion at Edgware Road in London
Proposals in the government's Counter Terrorism Bill could see a special coroner appointed for an inquest where national security is an issue.
The Justice Secretary could also ensure the coroner could sit in secret and without a jury.
Robert Webb, whose sister Laura died in 2005, said that families and society in general needed answers from inquests.
The clauses involved are clauses 64 and 65 of the Counter Terrorism Bill currently going through Parliament.
Those proposals are controversial and the worries of the 7/7 relatives will only add to the concerns, says BBC home affairs correspondent Daniel Sandford.
If it became law, it would allow the justice secretary to decide that an inquest needed special measures for reasons of national security.
The coroner could be replaced by a government-appointed coroner and could take place in secret, without a jury.
Families of those who died in the London bombings of 2005 have said they are worried the proposals would apply to the inquests of those who died.
Relatives want to use the inquests to ask what the police and MI5 knew about the bombers ahead of the attacks.
The government has confirmed it will not hold a public inquiry into the London bombings, which killed 56 people and injured about 800.
A group made up of survivors and relatives wanted an independent review of the way security agencies and others acted in the run-up to the attacks.
Robert Webb, whose sister Laura was killed in the Edgware Road bomb detonated by Mohammad Siddique Khan, said lessons had to be learned.
"It's a very worrying proposal. I think there are several reasons for that. The most important from the point of view of the brother of a victim of a terrorist attack is that we have a need to know what happened and if any lessons can be learned from the attacks.
"Clearly if parts of any inquest are going to be held in secret not only do we not get the answers but the wider public don't.
"It's my belief that society as a whole needs to be as well informed as possible about these attacks so we can all play our part in preventing them."
He also said that it was important to have a coroner who was independent of the government to look impartially at each case.
A date for the 7 July inquests has still not been set.
The Ministry of Justice said it would be unhelpful to speculate on whether the measures would apply in any specific case but they could be used in any inquest involving material that could not be disclosed publicly.
The Commons Justice Committee will call on the government to abandon the proposals.