LONDON (Reuters) – British foreign minister Boris Johnson will oppose any move to adopt European Union regulations made after Britain leaves the bloc in March 2019, the Sunday Telegraph newspaper reported, risking reigniting divisions over Brexit.

Johnson, who campaigned to leave the EU in last year’s referendum, is one of Britain’s highest-profile politicians and seen as a possible replacement for Prime Minister Theresa May. On Friday, he praised a speech by May in which she set out her plan for a roughly two-year transition period after Brexit.

But the Telegraph reported that Johnson had set out a new set of demands, reviving talk of a split among May’s senior ministers which has the potential to destabilize her minority government.

“Boris will be one of those Cabinet ministers pushing to make sure we don’t have any new EU rules and regulations during the transition,” a cabinet source was quoted as saying by the newspaper.

Johnson had fueled talk of a leadership challenge ahead of May’s speech by publishing his own 4,000-word plan for Brexit which was seen as a criticism of May’s more cautious approach.

May’s transition plan, set out in the Italian city of Florence in a speech that sought to break an impasse in negotiations with the EU, underlined the importance of regulation to the future economic relationship with the bloc.

She highlighted the fact that Britain and the EU start with identical regulatory standards and said she wanted “a practical approach to regulation that enables us to continue to work together in bringing shared prosperity to our peoples”.

She did not say whether she thought EU regulations passed during the transition period would be matched by Britain but said, on EU law, that British courts would be able to take European Courts of Justice rulings into account.

May’s Brexit minister David Davis said he did expect British and EU regulations to diverge over time after Brexit.