The European Parliament should oppose the start of talks on a trade arrangement with the U.K. if it’s not satisfied citizens’ future rights are protected, the legislature’s Brexit negotiator Guy Verhofstadt said. People moving to Britain from other European Union countries right until the day the U.K. leaves the bloc—and those who have lived there in the past—should have recourse to European courts to ensure British authorities aren’t violating their privileges, Verhofstadt, the parliament’s point man in withdrawal negotiations, told lawmakers Thursday in Brussels. The 28-nation assembly, which has a veto over the final exit deal, “must take its responsibility to decide if yes or no, there is sufficient progress to go from phase 1 to phase 2,” Verhofstadt said, referring to the passage from negotiations on the U.K.’s withdrawal from the bloc to preparations for a future trade pact. “We take as a key element for such an assessment citizens’ rights.” The EU has unveiled a series of demands it wants the U.K. to agree to as part of its deal for leaving the bloc. One of the most controversial is the European Court of Justice continuing to provide the final guarantee of entitlements for European citizens in the U.K. for the rest of their life. Prime Minister Theresa May has already promised Brexit will mark the end of the ECJ holding sway in the U.K. The protection of citizens’ rights should be based on “EU law on the one hand and the oversight of the European Court of Justice on the other,” Verhofstadt said. He added that he will “pressure” negotiators throughout the talks to ensure they get the best possible deal for European nationals, who move there before the U.K. leaves, including continued access to British health care, education and the labor market.