A Northern Ireland human rights organisation has lodged a formal complaint with the European Ombudsman over the question of how the rights of Irish citizens in Northern Ireland will be safeguarded post-Brexit, RTÉ News has learned.

The group claims that a promise by all sides in the Brexit negotiations to protect rights that derive from both the Good Friday Agreement and European Union law has been watered down as the negotiations have progressed.

The submission argues that Irish citizens in Northern Ireland will lose a wide range of EU rights, benefits and opportunities, including the right to vote in European Parliament elections.

The complaint comes amid growing concern among rights organisations and legal experts that human rights protections granted by both EU law and the Good Friday Agreement will be irrevocably weakened after Brexit.

Experts suggest that equality rights in Northern Ireland, as well as protections afforded by the European Convention on Human Rights and the EU's Charter of Fundamental Rights, could all be weakened as EU law is gradually replaced by British law.

The case lodged with the EU Ombudsman has been brought by the Committee on the Administration of Justice, a Northern Ireland-based human rights organisation, as well as three individuals, including two academics.

They say that any watering down of promises to uphold the EU rights of Irish citizens in Northern Ireland would mean they would become "second-class" EU citizens.

A spokesperson for the EU Ombudsman, Emily O'Reilly, has confirmed the office received the complaint on 20 September. Ms O'Reilly will decide within two weeks whether the complaint is admissible.

Specifically, the complaint states that a promise not to diminish the rights of Irish citizens in Northern Ireland was made by the EU and UK in the Joint Report of December 2017.

However, the complainants say that as the provisions of the Joint Report have been carried over into the draft Withdrawal Agreement, that commitment has been diluted.

A copy of the complaint, seen by RTÉ News, claims there has been "a significant and detrimental mistranslation of the commitments" made by both the European Commission and UK.

The submission claims this would inhibit freedom of movement, consular assistance from other EU countries when abroad, the rights to petition EU institutions, as well as the rights to vote, and stand, in European elections.

The submission highlights a number of paragraphs in the Joint Report, which specifically promise to protect rights of Irish, and therefore EU, citizens with the promise "that no diminution of rights" will be caused by Brexit.

Following the signing of the Joint Report, EU leaders instructed the European Commission to ensure that the "commitments" contained in it were "respected in full and translated faithfully into legal terms as quickly as possible".

However, the CAJ complaint says the promise of "no diminution of rights" has not been given full legal weight in the draft Withdrawal Agreement.

The submission points to paragraphs 42, 52 and 53 of the Joint Report as promising to uphold rights that derive from both the Good Friday Agreement and EU law.

In particular, Paragraph 52 states that "the people of Northern Ireland who are Irish citizens will continue to enjoy rights as EU citizens, including where they reside in Northern Ireland".

The complaint points out that the Withdrawal Agreement is required to give effect to such rights, and to allow Irish citizens in Northern Ireland to both "access" and "exercise" those rights.

However, the submission argues that promises have been watered down in several ways, including by placing some of the commitments in the preamble to the treaty, which is not legally-binding.

Another concern is that while the draft Withdrawal Agreement promises "no diminution" of those rights enshrined in the Good Friday Agreement under the heading Rights, Safeguards and Equality of Opportunity, the draft treaty does not give specific cognisance of the citizenship part of the Belfast Agreement.

However, the CAJ and the other complainants insist that the Joint Report promised "the continued exercise or access to almost all EU citizens' rights, opportunities and benefits, where that citizen resides in Northern Ireland".

The complaint says that EU leaders last December sought to make sure that the "arrangements required" for the ongoing exercise of these rights were "realised".

The CAJ essentially argues that while the Joint Report is generous in upholding the EU rights of Irish citizens, the Withdrawal Agreement, which will be legally binding, is much less so.

Other experts say it is unclear whether or not a range of EU equality laws, which currently apply in Northern Ireland, will be carried over.

One leading constitutional lawyer has said there is a commitment to include these laws in an annex in the Withdrawal Agreement, but that there are no details as to what those laws will include.

Another concern is that the British government has singled out the EU's Charter of Fundamental Rights as one piece of EU legislation that will not be transposed into British law as part of the Withdrawal Act.

The charter is legally binding on EU member states, and it requires a set of fundamental human rights to be observed when EU law is being applied.

Because it will no longer be part of UK law, there are concerns that this will weaken the protection of rights.

Many EU rights are only realisable when an individual crosses an EU border, i.e. to work, study, avail of healthcare, etc.

The CAJ argues, however, that Irish citizens in Northern Ireland should be entitled to exercise those rights "including where [qualifying persons] reside in Northern Ireland" and that Paragraph 52 of the Joint Report specifically tasks the European Commission to "give effect to the ongoing exercise of, and access to such EU rights, opportunities and benefits".

Sinn Féin MEP Martina Anderson was told by the European Commission in a written response to a parliamentary question in June that, even though they enjoyed certain EU rights, "Irish citizens in Northern Ireland will no longer benefit from United Kingdom's participation in [European] Union programmes, policies and activities when this participation ends following the United Kingdom's withdrawal from the Union".

The response continued: "Eligibility to vote and stand as candidates in elections to the European Parliament is determined by Irish law, which requires Irish citizens to be ordinarily resident in [the Republic of] Ireland."

A Government spokesman told RTÉ News: "This concerns a complaint to which the Irish Government is not a party, which has been lodged with the EU Ombudsman, and it would not be appropriate to comment on its specifics.

"As the Taoiseach made clear last week, after Northern Ireland leaves the European Union, everyone in Northern Ireland will still have the right to be an EU citizen.

"The Irish Government is determined to ensure that the Withdrawal and Future Relationship Agreements protect citizens' rights, both the rights of EU citizens living in the UK, and particularly EU citizens in Northern Ireland.

"That is also why Ireland wants to ensure that the Common Travel Area is retained, allowing Irish and British citizens to travel freely between Britain and Ireland to live, work, study, access health, housing and education in both countries."