"I respectfully regret to inform you that I will not be able to participate," the former European commissioner wrote in a letter to Jim Jordan, the Republican head of the House of Representatives' Judiciary Committee, that was shared with AFP.

"I have been informed that the European Commission will answer you directly," Breton said.

Brussels has adopted an unmatched legal arsenal aimed at reining in tech giants, with the Digital Services Act (DSA) focusing on content moderation and the Digital Markets Act (DMA) covering competition.

Both laws are under attack from Trump's Republicans, and the US leader -- without explicitly naming the EU -- threatened this week to impose new tariffs on countries with digital regulations that sought to "harm" US technology.

The EU has insisted in response on its "sovereign right" to regulate digital activities in the bloc.

Aimed at protecting consumers from disinformation and hate speech as well as counterfeit or dangerous goods, the DSA obliges platforms to remove or prevent access to illegal content.

Among its provisions, it instructs platforms to suspend repeat purveyors of hate speech -- something framed as "censorship" by US detractors.

Jordan announced Wednesday on X that his committee would hold a hearing next week entitled "Europe's Threat to American Speech and Innovation", with British hard-right leader and eurosceptic Nigel Farage named as a "confirmed" witness.

Breton, who served as the EU's powerful internal market commissioner from 2019 to 2024 with a sprawling brief including digital policy, was cited in Jordan's post as an "invited witness".

In his letter, Breton emphasised the need for a "respectful transatlantic partnership" -- and referred the lawmaker to an op-ed piece he published in several European newspapers on Thursday.

"Donald Trump's assault on Europe's democratic right to regulate tech is an outrage," Breton wrote in the article.

"How long are we, citizens of the EU, going to tolerate these threats? Submit to those who want to impose their rules, their laws, their deadlines on us?"

"The time has come to rise up. Europeans must stand together and proclaim loud and clear: 'Enough is enough'," Breton wrote.