As it is hard to identify 'main parties' (as that fluctuates quite considerably), let's discuss all parties elected into Parliament during the last elections.
According to the republicans themselves (who sent questionnaires to political parties in 2021 to learn more about their stance) so far there are three parties in favor or a republic:
- Socialist Party (9/150 seats) (although so far they've seemed to state the same that the new United Left-party leaders expressed: given that most people in the Netherlands value the monarchy, they are fine with a ceremonial role; expected to loose seats in the next elections)
- Green Left (8/150 seats) (one of the two parties that merged into the new United Left party; so most likely it were primarily members of this faction proposing and voting for the amendment; expected to gain seats among others due to their new party leader, former EU commissioner Frans Timmermans)
- Bij1 (1/150 seats) (an anti-discrimination party; most likely going to loose their one seat in the next elections)
They themselves are not sure about the stance of the Party for the Animals (6 seats); probably also in favor of a republic?! Officially, they'd prefer a 'modern monarchy'.
On the other hand, there are several parties clearly pro-monarchy:
- Liberal party (People's Party for Freedom and Democracy; VVD) (34/150 seats - currently by far the largest party and therefore main coalition party, expected to lose some seats but might still end up the largest; or at least one of the three largest)
- Christian Democratic Appeal (CDA) (15/150 seats - in government; expected to lose seats to the new New Social Contract (NSC) party of their former colleague)
- Christian Union (a christian left-center party; 5/150 seats - in government; expected to remain stable)
- JA21 (a populist right-wing party) (3 seats; might loose a seat)
- Reformed Political Pary (SGP; a christian-reformed right-wing party) (3/150 seats; expected to remain stable)
Source:
republiek.org