BRUSSELS—European lawmakers said Thursday that COVID-19 certificates aimed at facilitating travel across the European Union should be enough to move freely this summer, a position likely to clash with member states’ prerogatives in their upcoming negotiations. EU legislators said Thursday in their negotiating position on the European Commission’s proposal that EU governments shouldn’t impose quarantines, tests, or self-isolation measures on certificate holders. The EU’s executive arm proposed last month that the certificates would be delivered to EU residents who can prove they have been vaccinated, and also to those who tested negative for the virus or have proof they recovered from it. The European Commission’s goal is to boost travel from one member state to another during the pandemic. But since border control is a competence of member states, each of the 27 EU countries will remain entitled to add extra requirements for granting access to its soil. “What’s the …