The Ulster Unionist MP, Lady Sylvia Hermon, has accused the British government of "legalising discrimination" in recruiting for the new Police Service of Northern Ireland.
She has also expressed concern that the Human Rights Commission and the Equality Commission in the North regard "discrimination in police recruitment as justified".
In an address to the Ballinasloe Chamber of Commerce in east Galway, the North Down MP warned of a "seeping away" of support for the Belfast Agreement within the unionist community.
However, she also said she believed the majority of unionists failed to recognise the "significant step" taken by the IRA in decommissioning, "what a huge jump it was", and "how difficult it must have been to handle the change".
"I actually believe Gen de Chastelain when he says that we have witnessed an event which is significant," she said.
In a reference to the increase in paramilitary punishments, the majority of which were carried out last year by loyalists, she warned that loyalists had "fallen off the political radar screen".
Lady Hermon said she had signalled this even before last week's death of Mr Danny McColgan, whom she described as "a very decent, hard-working postman".
The loyalists had no political voice and were utterly ruthless, she said.
"Having stood strongly in support of the agreement, I have to tell you that I am deeply concerned about the seeping away of support among the unionist community," Lady Hermon said.
"There is absolutely no doubt in my mind that police reform was handled so insensitively that much of the original unionist support for the agreement has evaporated.
"Despite the fact, and it is a fact, that the vast majority of the 175 recommendations in the Patten report were based upon the RUC's own internal Fundamental Review, the Ulster Unionist Party is still being blamed for the so-called destruction of the RUC.
"Not only did changes to its title and badge cause deep offence throughout the unionist community, but the introduction of religious discrimination for recruits joining the new police service has only served to aggravate the difficulty of those changes."
However, it was "not all doom and gloom", she added, as the unanimous agreement on the composition of the badge represented progress.
"After years and years of anti-discrimination in Northern Ireland, the British government has now legalised discrimination in the recruitment of new police officers," she said.
"While all recruits must go through the same rigorous training and assessments to qualify for the recruitment pool, once they are in that pool the Chief Constable selects successful candidates on the basis that 50 per cent are of the Catholic faith, while the other 50 per cent are of any other faith or none at all.
"Such discrimination is deeply divisive and counterproductive. It is also demeaning, I believe, for good young Catholic recruits, who are rightly there on merit but who can have it endlessly cast up to them that they are there on the basis of their religion.
"The fact that the new Human Rights Commission and Equality Commission in Northern Ireland - both creations of the Belfast Agreement - regard such discrimination as justified has, of course, undermined from the very beginning any confidence that unionists might otherwise have had in these two institutions.
"The agreement promised equality of opportunity for all of us in Northern Ireland. All of us were supposed to be free of discrimination on grounds of political opinion and religious belief. That is what I voted for, but that is not what the Equality Commission, and the Human Rights Commission are delivering.
"No wonder the vast majority of unionists were suspicious of, and unenthusiastic about, the draft Bill of Rights published last September by the Human Rights Commission," she said.
Lady Hermon, who is wife of the former RUC chief constable, Sir John Hermon, warned that the current strength of the police service, at 7,200 full-time officers, was below the approximate size of 7,500 recommended by Patten.
"This is, I believe, a dangerously low level especially since loyalist and dissident republican paramilitaries continue to be so murderous and hell-bent on wrecking the agreement," she said.
The Ballinasloe function is Lady Hermon's second visit to the South in the last two months, amid continued criticism of her pro-agreement stance among colleagues.
When she stood in last June's British general election, she was dismissed as a "fur-coat unionist" by her rival, the sitting MP, Mr Robert McCartney, but she went on to take the seat in North Down.
Last month she spoke about being an "endangered species" as a supporter of the Belfast Agreement, when she addressed a Fianna Fáil constituency meeting in south Dublin.