Discord has surfaced on the eve of a European Union summit where 27 of the bloc's leaders are seeking a united front in exit negotiations with Britain.

The nations are set to give the lead role in the talks to EU Commission pick Michel Barnier and the EU Parliament fears it will be sidelined, the legislature's chief said Wednesday.

Parliament President Martin Schulz is warning that legislators could reject any Brexit draft agreement and that it could lead to "the very hardest of Brexits."

Schulz will be able to make his complaint directly to the 27 leaders during Thursday's summit. Once British Prime Minister Theresa May departs from the meeting, the remaining 27 will dine together to hammer out a united stand.