The European Parliament is seeking a new role: taking a lead in a possible Brexit battle with the U.K.

“The Parliament is ready to play the bad cop,” said Pedro Lopez de Pablo, spokesman for the European People’s Party (EPP), the largest group in the chamber. “We are going to be those who will complain about almost everything."

Though it is not formally part of the upcoming divorce negotiations, Parliament is ready to disrupt the talks by leaning on its veto power over the Brexit deal if London doesn’t respect the principles the European Union is founded on, officials said.

“The Parliament will be a moral authority on Brexit,” said Jean Arthuis, a French MEP and president of the Budgets Committee. “It will be a tool to keep citizens informed, and nothing is better than public opinion to weigh on governments.”

Since the U.K. is likely to “divide Europeans” in order “to complicate things," according to Arthuis, "Parliament will have to control the executive power [and] so it is our role to make sure it does.”

The power to veto — and annoy by resolution

While Parliament won't negotiate any Brexit deal with the European Council or European Commission, MEPs will have to consent to the final withdrawal agreement, giving them veto power.

The resolution will "send a signal to the U.K. that nobody will benefit more than the other" — Philippe Lamberts, president of the Greens

Furthermore, MEPs can issue non-binding resolutions “on the state of negotiations,” which will allow them to put pressure on the Commission and on EU governments, an official said.

In the past, Parliament has used its veto to scuttle important pieces of legislation, as in 2012 when it rejected the Anti-Counterfeiting Trade Agreement (ACTA), an international treaty to crack down on digital piracy.

This week, Parliament is expected to showcase its uncompromising approach toward the U.K. with a resolution that will be finalized after British Prime Minister Theresa May triggers Article 50 to formally exit the EU on Wednesday. MEPs are expected to adopt the resolution at a plenary session in April.

“If the Brits on Wednesday announce that they have no intention to comply with their budget obligations, there will be retaliations,” said an EU official said, referring to the so-called divorce bill.

Such retaliation could include barring the U.K. from the customs union, “which means that they might have to import Parmesan from New Zealand or Canada,” said an EU official.

It might also mean stripping Britain of so-called passporting rights that allow its banks and other financial firms to sell their services throughout the bloc and giving those based in the EU similar access to the U.K.

Though the resolution is still a work in progress, Philippe Lamberts, president of the Greens, said it will urge London to preserve the reciprocity of rights between U.K. and EU citizens, as well as “reassert the conditions of access to the single market,” preserve the Good Friday agreement with Ireland and ensure the U.K. is still bound by European Court of Justice rulings after it leaves the EU.

“The resolution will be firm on the principles but it will not be revenge-driven," Lamberts said. “It will set the right tone, and send a signal to the U.K. that nobody will benefit more than the other; that we are interdependent."

Sources say further resolutions are likely to canvass the future status of British MEPs and officials in the EU after Brexit.

Parliament is the most pro-European institution, Lopez de Pablo said, "so it will be very tough," especially when it comes to "the freedoms included in the treaties," such as movement of goods, workers, services and capital.

Gianni Pittella, president of the Progressive Alliance of Socialists and Democrats (S&D), said reciprocal rights for U.K. nationals living in the EU and EU citizens in the U.K. is a “pre-condition for starting talks about the future relationship between the U.K and the EU.”

Bringing the guns

ALDE leader Guy Verhofstadt, who leads the Brexit file for Parliament, won't be alone in his role as top cop. Parliament has more than 20 people working on Brexit, including Markus Winkler, its main sherpa, Nick Lane, director for Inter-institutional Affairs and Legislative Coordination, as well as Anthony Teasdale, the director general of the European Parliamentary Research Service.

In addition, each of the main pro-European political groups, including the EPP and S&D, have MEPs working on Brexit, including Vice President Esteban González Pons and Elmar Brok, a well-known German MEP. Each of the 21 committee secretariats also has a person in charge of Brexit.

The Parliament has drafted a plethora of documents on the more than 20,000 laws and regulations that will need to be negotiated in the next two years. (Details from 21 different committee reports obtained by POLITICO can be found here.)

Some of the toughest recommendations came from the Committee on Civil Liberties, Justice and Home Affairs, which urged the U.K. to abide by European Court of Justice (ECJ) rulings after it leaves the EU and argued the bloc’s highest court should have its reach extended for a transitional period after Brexit.

That was in response to May’s announcement the U.K. would no longer fall under the jurisdiction of the ECJ. Britain, she said recently, “will not have truly left the European Union if we are not in control of our own laws."

But while resolutions and recommendations have the power to annoy, Parliament's greatest weapon remains the veto.

“If there are no agreement or not a consent on the outcomes of the negotiations, there is simply no deal,” said a Commission official. “Everybody has an interest in reaching an agreement in the end.”

Giulia Paravicini contributed to this article.