Will Finland have to ratify Sweden's NATO accession?

Question

The original plan was for Finland and Sweden to join NATO at the same time. It has since become clear, however–due to opposition from Turkey and Hungary–that Sweden and Finland will not be joining at the same time. There are separate Accession Protocols for Finland and Sweden, each of which has to be ratified separately by all member states. While all the other member states ratified both protocols together, Turkey and Hungary have decided to ratify Finland's protocol now, but hold off on ratifying Sweden's for the time being.

Given those decisions, Finland's accession process is almost certain to be formally completed in the next few days, at which point Finland will be a full member of NATO. But there will now be a period in which Finland is in while Sweden is still out, and we don't know how long that period will last. It is likely that, given a few more months, Turkey and Hungary will be convinced to drop their opposition – but that's only likely, not guaranteed.

Does that mean, once Finland has finished joining NATO, it is going to have to formally sign and ratify Sweden's accession protocol? If every existing member state has to ratify each accession protocol, doesn't that now mean Finland has to ratify Sweden's as well? And normally, to ratify something, you first have to sign it: will they have to formally reopen Sweden's protocol to add Finland's signature?

I have no doubt that, if it is required, Finland would promptly sign and ratify it – politically, Finland is a strong supporter of Sweden's membership – my question is only about the legal formalities involved.

Answer 1

Not separately to Finland's ratification of its own accession - according to Henri Vanhanen, a research fellow at the Finnish Institute of International Affairs;

The Parliament doesn’t have to [ratify Sweden's ascension]: it already approved Sweden when it voted in favor of the government NATO legislation — it was included in the government proposal/legislation/FAC report. Checked with the Finnish MFA legal department.
_{Twitter, March 17th, 2023}

This was later confirmed by members of the Foreign Affairs Committee to Ilta-Sanomat, who pointed to the following passage in the report of the FAC which was approved by Parliament on March 1st:

Parliament approves the North Atlantic Treaty signed in Washington on April 4, 1949 referred to in the government's motion HE 315/2022 vp, as amended by the accession protocols signed by July 5, 2022, and the agreement on the status of the North Atlantic Treaty Organization, national representatives and international personnel made in Ottawa on September 20, 1951 agreement.

The bill approves the NATO treaties as amended by the July 5th accession protocols which approve both Sweden and Finland's membership - so by Finland's ratification of the treaty, they are also approving Sweden's membership without having to ratify it separately after joining.

The secretary of the FAC, Tiina Larvala, predicted that "Finland's accession document and the document with which Finland ratifies Sweden's membership will be stored separately in Washington", but the Finnish Parliament is not required to approve Sweden's accession after Finland formally joins the alliance.