The final election rally of the European People's Party took place in Munich on Friday with German Chancellor Angela Merkel receiving a warm reception.
Lead candidate, Manfred Weber, made a declaration of war on nationalists and populists as mainly moderate blocs faced competition from hardline parties.
He said: "The clouds on the horizon are a lot about trade, Brexit - which creates insecurity - and the behaviour of American President Trump. And that is why we, as Europeans, have to take a clear position."
Austrian Chancellor Sebastian Kurz was due to attend but spoke via videoconference instead following the political scandal in his own country last week.
Meanwhile, in Barcelona, the lead candidate of the Party of European Socialists, Frans Timmermans, was also campaigning with Spain's prime minister, Pedro Sanchez.
He said that the surprising first-place finish by his party in the Netherlands would push the Socialists to victory across Europe.
The centre-right EPP holds the presidencies of the Commission, Council and Parliament — a monopoly which socialists and Liberals hope to break.