Brussels breathed a hearty sigh of relief at Emmanuel Macron's commanding victory in the French election, but it shouldn't expect things to carry on unchanged as the new president has ambitious reform plans.

In Macron, the EU has an unusually fervent pro-European leader who put strengthening the European project at the center of his campaign. "I will defend Europe," he said in his first victory speech on Sunday. "It is our civilization that is at stake."

However, the former economy minister is proposing deep changes, notably to the way the eurozone operates. Here's what his presidency is likely to mean for Brussels and the EU:

First things first: the economy

To reassure Brussels and his EU partners, Macron's first test will be to pass domestic labor reforms which are recommended by EU finance ministers, something he has promised to do in the first weeks of his presidency. Macron will also need to respect the 3 percent deficit rules required by the EU — a pledge he also made during the campaign.

His supporters in Brussels should not expect him keep to the existing course. On trade, Macron has pledged EU-wide protectionist measures and called Germany to curb its trade surplus.

In his final day of campaigning before voting Sunday, Macron also told the French news website Mediapart that he was "in principle" in favor of concerted Greek debt relief "to keep Greece in the eurozone." That approach would put him at odds with some Northern European countries.

EU reform

Though an evangelist for the EU, Macron — like many of his predecessors — spoke repeatedly during the campaign about the need to reform the way the bloc operates, especially the eurozone.

He wants new fiscal and social rules for the eurozone to bind its constituent economies closer together and prevent future crises. He wants a new parliamentary assembly of the eurozone composed of EU and national lawmakers; a eurozone budget; and a eurozone finance minister.

More broadly, he has also pushed for pan-European ballots at the 2019 EU parliamentary elections for the 73 seats left vacant by the Brits after Brexit.

Tough line on Brexit

Macron has shown no signs of being a soft touch on Brexit. “An exit is an exit,” he told reporters in Downing Street after an hour-long meeting with Theresa May in February. “Brexit can’t lead to a kind of optimization of Great Britain’s relation with the rest of Europe,” he added.

According to French news reports, Macron also said there wouldn’t be any access to the single market “without budgetary contribution.” “I will be very committed on my side to make sure that there will be no undue advantages,” he told France 24 TV channel.

France’s priority goals in the Brexit negotiations, he added, would be to “protect the interests of French people and of Europeans.” On Monday morning, his economic advisor Jean Pisani-Ferry re-emphasized the message, telling BBC Radio 4 that Macron would be “tough” on Brexit negotiations, but would not seek to punish the U.K.

Sanctions against Poland?

Though he didn’t use the the S-word, Macron has said he would be tough on Poland and Hungary for their recent breaches to EU rules. In an interview with French regional newspaper La Voix du Nord, Macron said “a decision” on the Polish issue would be taken “in the three months following my election.”

“We can’t have a Europe ... [that] decides to do nothing when faced with one EU member behaving like Poland or Hungary" — Emmanuel Macron

The EU should take action against Poland, he said, because it “exploits fiscal and social gaps inside the EU” and “breaches all principles of the Union.” The logical punitive step would be to trigger Article 7 of the Lisbon Treaty which would withhold Poland's voting rights in the Council.

“We can’t have a Europe which debates on every decimal of each country’s budgetary issues but decides to do nothing when faced with one EU member behaving like Poland or Hungary, on issues like university and knowledge, refugees, fundamental values,” he said.

Boosting the center

Though Macron has not hitched his party En Marche to the wagon of liberals and center-left parties in the European Parliament, many of them hope he will join them in the future. That would give momentum to the Liberals in Brussels who believe in the emergence of a great European centrist party.

Following Macron's victory Sunday, Guy Verhofstadt, the president of the liberal ALDE party in the Parliament, said in a video posted on Twitter that "all the European progressive forces expect France to initiate a new European deal." If Macron’s En Marche joins ALDE, it would give the fourth-largest group in the Parliament more members and more influence in the 2019 European elections.

Macron’s appeal goes beyond the centrists, as many Socialist MEPs expressed support for him following the first round of the presidential elections. However, it remains unclear whether French Socialist MEPs would rally behind En Marche in June's legislative elections. On Sunday, Christine Revault d’Allonnes-Bonnefoy, president of the French Socialist delegation in the European Parliament, said only France's Socialist program, with its balanced fiscal policy and focus on a “social Europe ... can allow our children to live better than we do."