Refugee and human rights groups have expressed disappointment at the Supreme Court decision, which they predict will lead to cases before the European Court of Human Rights.
The court ruled yesterday that two sections of the Illegal Immigrants (Trafficking) Bill, 1999, referred to it by the President, Mrs McAleese, do not contravene the Constitution.
The Irish Refugee Council (IRC) said the provision in Section 10 of the Bill for the detention of failed asylum-seekers for up to eight weeks was excessive.
The chief executive of the IRC, Mr Peter O'Mahony, said detention of unsuccessful asylum-seekers was undesirable and should be used only as a last resort.
"The Irish Refugee Council accepts that very limited pre-deportation detention may be necessary in exceptional circumstances, as determined by a judicial procedure and subject to review," he said.
"However, detention for a period of up to eight weeks is excessive, especially as the decision to detain is not instigated by a member of the judiciary."
Mr O'Mahony condemned the Bill's reduction to 14 days of the time failed asylum-seekers can apply for judicial review of deportation orders, as Irish citizens have six months to start such a legal action.
"This amounts to an unacceptable, unjustified and discriminatory restriction on the right of non-Irish nationals to access to, and relief of, the Irish courts," he added.
Mr O'Mahony said the IRC believed the proposed measures may conflict with the European Convention on Human Rights.
The Irish Council for Civil Liberties (ICCL) said the court's reasoning in upholding the constitutionality of the Illegal Immigrants (Trafficking) Bill, 1999, was "minimalist and unduly non-interventionist as regards the rights of failed asylum-seekers".
Its director, Mr Donncha O'Connell, claimed the part of the court's decision dealing with "preventive detention" of failed asylum-seekers under Section 10 of the Bill was "particularly disappointing and unconvincing, but it is to be hoped that the appropriate authorities will take due regard of the court's emphasis on the safeguards which exist for detainees in such situations".
Mr O'Connell said it would now become common for asylum-seekers facing deportation to apply for an extension of the new 14-day time limit in which to apply for judicial review of the decision.
"This raises the obvious question as to why such an additional hurdle was put in the way of asylum-seekers in the first place," he added.
Mr O'Connell said it would still be open to individuals to challenge the operation of the sections of the Bill before domestic courts and to take cases to the European Court of Human Rights.
The Labour Party's justice spokesman, Mr Brendan Howlin, said he was disappointed that the "manifestly discriminatory" provisions added to the Bill at the last minute were not held to be in breach of the Constitution. He said it seemed that the two-week deadline would deprive those in need of court protection and would not work in practice.
"It is a great pity that this issue had to be decided in the abstract on a once-and-for-all basis, rather than by reference to the facts of specific cases," he added. Mr Howlin said the Minister for Justice, Mr O'Donoghue, should "publish and implement a fully thought-out and coherent policy in relation to the whole area of asylum and immigration rather than relying on ad hoc, crisis-driven responses".
With regard to new detention powers, he asked how the State would deal with family units. "Where will [the Minister for Justice] accommodate children and young people who have been separated from their parents?" he said.
The Green Party MEP, Ms Patricia McKenna, said she was deeply disappointed at the Supreme Court's decision and hoped that individuals would avail of their right to challenge and monitor its implementation.
"I also hope that the planned incorporation of the European Convention on Human Rights into Irish Law will improve the current level of protection for asylum-seekers," she said.
Ms McKenna said it was unfair that asylum-seekers should have only two weeks to seek a judicial review when an Irish citizen had six months.
"There is something seriously wrong with our Constitution if it cannot afford all people equal rights of access to the courts and surely it is our Constitution that should be amended to reflect modern-day reality," she added.
A spokesman for the Department of Justice said the Minister welcomed the Supreme Court judgment and was "pleased to have been in the position to reform our immigration laws to reflect modern-day reality".
The court's ruling was also welcomed by the Immigration Control Platform, which said it hoped to see a rise in the "risible number of failed asylum-seekers deported".
According to Garda sources, it is likely that the practice of detaining asylum-seekers in Mountjoy Prison or its training unit will continue. The State is entitled to detain failed asylum-seekers in any Garda station, but this rarely occurs.
About 60 asylum-seekers have been deported since last November, and some 440 deportation orders remain outstanding.