Some of the United States’ closest allies, the UK, Germany and France, have formed a united front to defend the 2015 nuclear deal, CNN reported on Tuesday.

Without being invited, they’ve organized a joint team to travel to Washington this week, setting up their own meetings to ramp up the pressure on the U.S., according to a senior diplomatic source from one of the participating countries.

The team of senior European diplomats will meet with members of Congress, the State Department and possibly at the White House on Thursday and Friday, the source said.

The visit continues an extended pressure campaign by key European nations, which has included visits from senior figures, including the EU foreign policy chief and UK foreign secretary, to protect the Iran nuclear deal in the face of hostility from President Donald Trump, who has declared he wants the agreement changed or canceled.

The nuclear agreement was signed by Iran, the European Union, Germany and the five permanent members of the UN Security Council – the United States, Britain, France, China and Russia – in July 2015. It took effect in January 2016.

The U.S. under the Trump administration is the only party which has made repeated attacks against the nuclear deal. In his new Iran strategy declared on October 13, Trump decertified the nuclear deal and asked Congress to decide about the fate of the agreement.

The U.S. administration has called for a renegotiation of the nuclear agreement, a request vehemently rejected by all other parties.

According to the nuclear agreement, officially called the Joint Comprehensive Plan of Action, Tehran agreed to put limits on its nuclear activities in exchange for termination of economic and financial sanctions.

The International Atomic Energy Agency, the United Nations’ nuclear watchdog, has been tasked to monitor Iran’s compliance to the deal.

Since the deal went into effect in January 2016 the IAEA has regularly issued nine reports each time confirming Iran’s adherence to the international deal.