The home secretary has published the grounds on which foreigners considered to be promoting terrorism can be deported or excluded from the UK.
Charles Clarke issued the list of "unacceptable behaviour" by those said to indirectly threaten public order, national security, or the rule of law.
The grounds, drawn up after the 7 July London bombings, include provoking and glorifying terrorism.
But civil liberty groups fear deportees could be tortured in their homelands.
Amnesty's Halya Gowan said: "The vagueness and breadth of the definition of 'unacceptable behaviour' and 'terrorism' can lead to further injustice and risk further undermining human rights protection in the UK."
And the Muslim Council of Britain (MCB) says the list of "unacceptable behaviours" is "too wide and unclear".
'Preachers of hate'
After the attacks in London, which killed 52 people, "the rules of the game" changed, according to Mr Clarke.
He ordered an immediate review of his powers to exclude and deport people, saying he wanted to ensure that any non-British citizen suspected of inciting terrorism was deported immediately.
Publishing the results of that review he said the first deportations could happen "very quickly - in the next few days".
"Individuals who seek to create fear, distrust and division in order to stir up terrorist activity will not be tolerated by the government or by our communities," said Mr Clarke
"By publishing the list today I make it absolutely clear that these are unacceptable behaviours and will be the grounds for deporting and excluding such individuals from the UK."
As part of a raft of measures to crack down on "preachers of intolerance and hatred", a new database will be drawn up of foreign-born radicals accused of encouraging acts of terrorism.
The global database will list those who face automatic vetting before being allowed into the UK.
It will also list "unacceptable behaviour", such as radical preaching and publishing websites and articles intended to foment terrorism.
Articles already published, as well as speeches or sermons already made, will be covered by the new rules.
A number of radical Islamic clerics could fall foul of the new measures.
Less than a week after the controversial cleric Omar Bakri Mohammed left Britain for Lebanon, Mr Clarke announced he would not be allowed back.
Others who could come under scrutiny include Mohammed al-Massari, the Saudi Arabian dissident whose website carried images of attacks on British troops in Iraq.
'Shuffled around world'
The government is still seeking assurances from several countries that no-one it deports will be ill-treated, but critics say such agreements are worthless and anyone suspected of supporting terrorism should be put on trial in this country.
Gareth Crossman, of the human rights group Liberty, said: "What separates us from the terrorists is that we do not torture people or send them to be tortured.
"We believe it is far better for terrorist suspects be tried than shuffled around the world.
"If it is necessary to deport people, we need more than self-serving assurances to demonstrate that countries with appalling human rights records are safe."
While the Home Office insists it will not deport people if there is a real risk they could be harmed, the plan has also been criticised by a UN expert on torture.
Manfred Nowak, UN special rapporteur on torture, said on Tuesday that agreements with countries which might have committed human rights abuses in the past was "not an appropriate tool to eradicate this risk".
Criminalisation of thought?
In response a Home Office spokesman said: "We believe a memorandum of understanding is a good example of the sort of international co-operation necessary to confront and defeat terrorism."
The MCB meanwhile said: "It would be more prudent to bring persons who threaten the peace and security of the realm, whether resident or visiting, to trial under our own laws.
"Sending them out may turn them into unwanted heroes who may then be free to export their vile thoughts, if such be the case, from exile. We do not want this."
The Islamic Human Rights Commission meanwhile issued a statement saying: "The IHRC views the new grounds for deportation as the criminalisation of thought, conscience and belief."