Some people are concerned that, although the government has proposed a clear 12-week time limit for access to abortion on request, (more details here) a future constitutional challenge could require that time limit to be lifted, so that abortion on request would be permitted up to viability.
However, at the present time, it is unlikely that a future Supreme Court decision would require substantial change to that time limit.
We cannot foresee in detail what cases might come before the courts if the referendum is successful and legislation is passed along the lines proposed by the government.
Historically, women have not brought abortion cases to court in Ireland; the decided cases on abortion largely concern women living in the care of the state who were unable to travel for an abortion abroad. It is theoretically possible that a case might be brought to challenge the time limit in principle, or to challenge the failure to provide in legislation for the time limit to be extended in particularly difficult cases where a woman misses the deadline for abortion on request.
However, there are three significant obstacles to wide-ranging constitutional challenge to abortion legislation. These are:
(i) the presumption of constitutionality
(ii) the absence of an independent constitutional right to abortion after repeal and
(iii) the constitutional position that the legislature ordinarily decides how individual rights should be balanced against public policy goals.
Presumption of Constitutionality
All Acts of the Oireachtas are presumed constitutional. This explains why the Supreme Court rarely strikes down legislation. The threshold for striking legislation down is very high. In Touhy v. Courtney  3 I.R. 1 at 47 the Supreme Court held:
the role of the courts is not to impose their view of the correct or desirable balance in substitution for the view of the legislature as displayed in their legislation but rather to determine from an objective stance whether the balance contained in the impugned legislation is so contrary to reason and fairness as to constitute an unjust attack on some individual’s constitutional rights.
In 2013, in Fleming v. Ireland  IESC 19 the Supreme Court held that the threshold is even higher where contested social issues are at stake:
[t]he presumption may be regarded as having particular force in cases where the legislature is concerned with the implementation of public policy in respect of sensitive matters of social or moral policy. (para 95)
Abortion is likely to be considered a ‘sensitive matter of social or moral policy’ for many years. Time limits in any abortion legislation will be presumed constitutional, and that presumption will be especially difficult to displace.
A Constitutional Right to Abortion?
It is highly unlikely that the proposed replacement for the 8th Amendment, called the 36th Amendment , creates a constitutional right to access abortion as such.
The text of the 36th Amendment says that “provision may be made by law for the termination of pregnancy”.
Here the presence of the word “may” rather than “shall” arguably suggests that there is no absolute constitutional right to abortion that could compel the government to pass abortion law. However, it is clear that any abortion legislation that is passed must be constitutional.
A constitutional provision permitting law to be made to regulate a particular activity does not necessarily create a corresponding right. For example, Article 42A of the Constitution says that “provision shall be made by law for the adoption of children” in certain circumstances, but this did not create an absolute “right to adopt”. The state did not lose its entitlement to regulate who may and may not adopt children when Article 42A passed.
Although women would not have a general constitutional right to access abortion after the referendum, other constitutional rights might be violated by disproportionately restrictive regulation of abortion access.
Currently, the 8th Amendment as interpreted in Attorney General v. X  IR 1 prevents consideration of any of the woman’s rights except the right to life. If the 8th Amendment is removed, a woman’s other constitutional rights would become relevant, including the right to privacy, to bodily integrity, to liberty, to equality and to freedom of conscience.
With the exception of the right to freedom from torture, none of these is absolute. The state is entitled to restrict them in the interests of the common good, including to promote the respect that is due to foetal life in its laws and regulations. (Alternatively, the former Chief Justice, Ronan Keane has recently suggested that the foetus might retain a right to life even without the 8th Amendment. However, this right would be more limited than under the 8th Amendment, and claims made under that right would need to be balanced against the constitutional rights of the woman).
This means, in principle, that the state is entitled to impose gestational time limits on access to abortion, and provide that, after those time limits have elapsed, abortion may only be accessed on certain grounds. (See further discussion here and here).
Balancing Individual Rights and Public Policy Objectives
In general, the Oireachtas decides how best to balance protecting individual rights with important public policy objectives (for example, the protection of foetal life in the interests of the common good).
The Oireachtas enjoys a wide discretion in selecting its policy objectives, even in times of social change (MD v. Ireland  1 I.R. 697 at 719).
Legislation is constitutional unless it disproportionately infringes on constitutional rights (Heaney v. Ireland  3 I.R. 593). It is likely to be very difficult to show that an element of abortion legislation strikes the wrong balance between individual rights and the common good. The courts will not simply substitute their assessment of the merits of legislation for the government’s own assessment. In Ryan v Attorney General  IR 294, (p. 212-213) Mr. Justice Kenny explained:
When dealing with controversial social, economic and medical matters on which it is notorious views change from generation to generation, the Oireachtas has to reconcile the exercise of personal rights with the claims of the common good and its decision on the reconciliation should prevail unless it was oppressive to all or some of the citizens or unless there is no reasonable proportion between the benefit which the legislation will confer on the citizens or a substantial body of them and the interference with the personal rights of the citizen.
As part of assessing whether an element of legislation is a proportionate infringement on individual rights, a court will consider whether the time limit is “minimally invasive” of women’s rights. This does not mean that it must be shown that the time limit may only restrict women’s access to abortion to a very minor degree – if that were the case, it would be almost impossible to regulate abortion at all. It means that the court should consider whether another measure was available which could have achieved the government’s aims without infringing so much on women’s relevant constitutional rights.
In considering whether the 12-week time limit is a proportionate infringement on women’s constitutional rights, a court would bear in mind that the Oireachtas is ‘uniquely well-placed’ to undertake a ‘careful assessment of competing and complex social and moral considerations’ (Fleming v. Ireland  IESC 19, ). This principle applies, not only where the court is considering an outright prohibition of any activity, but also where the court is considering legislation which permits and regulates, an activity as the government currently proposes to do with abortion (see for example MR v. An tArd- Chláraitheoir  IESC 60).
Based on established precedent, it seems likely that a court would defer to the Oireachtas’ judgment on the appropriateness of a 12-week time limit.
Even if they did not, the effects would likely be narrow and contained. In striking down a time limit, a court would not need to strike down the legislation in its entirety.
A finding that a 12-week time limit was invalid would not mean that any and all time limits for abortion access were invalid.