Call it the Brexit divorce court warning.

Even as EU leaders plan to extend an olive branch to London by starting internal discussions about a future trade relationship, France and Germany have pushed to include a reference to the jurisdiction of the European Court of Justice (ECJ) in draft conclusions prepared for next week's European Council summit, according to three EU diplomats.

The future role of the ECJ has been a major obstacle in the negotiations over a withdrawal agreement, with Brussels demanding that the court retain authority over any future disputes on citizens' rights and Britain adamant that its own courts take control and that it will not be bound by future judgments from Luxembourg.

The push by Germany and France, the EU's biggest and most powerful members, to include such language in the first paragraph of the draft conclusions (before any other Brexit issues are mentioned) is a reminder to London that the first phase of Brexit negotiations is nowhere near completed and that the divorce terms are not settled.

It is a particularly sharp jab considering there is general agreement that negotiators have made better progress on citizens' rights and Ireland than on the financial settlement.

At the end of the fifth formal round of negotiations last week, Michel Barnier said the two sides were in "deadlock."

The two European powerhouses pushed for the reference to the ECJ during a meeting of EU ambassadors on Friday night, and diplomats from other nations said it would likely be included in the final conclusions to be approved by leaders at the summit.

“They suggested a reference to the jurisdiction of the Court of Justice and most probably it will be reflected in the text,” one diplomat said.

Another senior diplomat said that mentioning the court by name was not needed to convey the EU's position but doing so would put emphasis on the priority of the issue for some leaders. "Jurisdiction of the ECJ is implicit in the original text, the EU law," the senior diplomat said. "It is not strictly necessary to mention it specifically, but it may be done."

A third high-ranking diplomat said the European Commission was behind the change as much as Berlin or Paris. "It was a proposal made by the Commission, which nobody opposed," the diplomat said.

Four diplomats told POLITICO that Germany and France decided to take a hard line on the role of the court and did not expend much energy on the line in the draft conclusions intended as an olive branch to London, in which the EU27 are called upon to “start internal preparatory discussions” on a future trade relationship and potential transition arrangements.

EU leaders seem prepared to authorize the start of internal discussions despite a lack of sufficient progress on the main divorce issues. The Council has said such progress is required before it will allow negotiators to move on to the second phase of talks. At the end of the fifth formal round of negotiations last week, the EU's chief negotiator, Michel Barnier, said the two sides were in "deadlock" over the financial settlement.

Diplomats said that Germany and France did not resist the language on internal discussions, which other nations supported as a way of making clear that Brussels was also eager to get to the next stage of talks.

"There's no challenge to 'internal preparatory discussion or work' at this point," one diplomat said.

"The discussion was mainly about whether or not this internal preparation should be made public or not," another diplomat said. "Diplomats agreed that the clock is ticking, and since sufficient progress has not been made, there isn't much time left so preparations are needed."

Another contentious point for leaders when they meet in Brussels on Thursday and Friday may be a section of the draft conclusions that declares EU leaders will "adopt additional guidelines" for Barnier should the Council find "sufficient progress" has been reached by its December summit. Such language appears to obligate the Council to quickly issue new guidelines, which in fact could prove difficult to do in a way that maintains the unity of the 27.

"This does not necessarily mean that European Council will adopt such guidelines immediately upon recommendation from the chief negotiator,” said one of the senior diplomats. Leaders "may want to take some time to look into the progress achieved before proceeding. In short: It is the EU27 that will trigger phase two, not the chief negotiator."

At Friday's meeting, diplomats also discussed plans for the Commission to “prepare position papers" on post-Brexit dealings with the U.K. "which will then be discussed in working groups,” one diplomat said. “The topics are obvious — it will be about the trade or the external relation dimension of our future relationship," the diplomat said.

The draft conclusions will be discussed by Europe ministers at a meeting on Tuesday before EU leaders sign off on them at a summit on Thursday and Friday. Approval requires the unanimous support of all 27 countries, and any one country can block the conclusions or insist on changes.