Spain's Constitutional Court issued an extraordinary preliminary ruling late on Saturday evening that forbids Carles Puigdemont from participating via Skype in a confidence debate in the Catalan Parliament, scheduled for Tuesday, to reappoint him as First Minister of the Spanish region.

Neither may Mr. Puigdemont vote by proxy, the court said, in a unanimous decision, and nor may another MP stand in for him during the debate.

The ban on proxy votes from abroad is also applicable to the other four regional representatives with Mr. Puigdemont in Brussels, because they also have arrest w...