Emergency laws ending the early release of people convicted of terror offences should have applied in NI, Stormont's justice minister has said.
Last week MPs passed the Terrorist Offenders Bill.
It means terror offenders in England, Scotland and Wales will only be considered for release once they have served two-thirds of their term.
Naomi Long said she believed there should have been "no barrier" to extend it to NI.
The bill was introduced in response to an Islamist-related terrorist incident in London last month.
The attacker, Sudesh Amman, had been freed from prison 10 days earlier.
Speaking in the NI Assembly on Monday, Mrs Long said her department had indicated to the Ministry of Justice (MoJ) in London that its preference would be for the law to be applied UK-wide.
"I made it clear that was my preference because I was concerned there would be a risk of a two-tier system when it comes to the paroling of terrorist prisoners being set up within the UK," she said.
She said ultimately the decision was taken by the MoJ to exclude Northern Ireland.
"Our first sight of that decision was the press release issued by the ministry in respect of that legislation, however there will be opportunities for NI to be included in a wider counter-terrorism bill so the door has not completely closed on that chapter," added the minister.
Westminster sources had indicated that the government would not apply the legislation in NI because the sentencing arrangements are set differently and any change could have legal ramifications.
At present, offenders who receive standard determinate sentences for terror convictions are released automatically after serving half their sentence.
The new legislation is being fast-tracked through the House of Commons.
The aim is to prevent the 28 February release of Mohammed Zahir Khan, who is the next convicted terrorist due to be freed after serving half his sentence for encouraging terrorism.