A report by a congressional committee in the United States has found four major global digital companies have used their market dominance in "anti-competitive and abusive ways" that have "weakened democracy".

The House Judiciary committee's subcommittee on Antitrust, Commercial and Administrative Law said it had sought answers from the chief executives of Apple, Facebook, Google and Amazon, but accused the senior executives of being "evasive and non-responsive". 

The report, which was released online this evening, said that Tim Cook of Apple, Jeff Bezos of Amazon, Mark Zuckerberg of Facebook and Sundar Pichai of Google headed companies which have "exploited, entrenched, and expanded their power over digital markets in anti-competitive and abusive ways". 

The subcommittee said that the global tech companies engaged in "predatory pricing" and other abusive practices.

"They not only wield tremendous power, but they also abuse it by charging exorbitant fees, imposing oppressive contract terms, and extracting valuable data from the people and businesses that rely on them," the report said.

The scathing 449-page report describes dozens of instances where the companies misused their power, revealing corporate cultures apparently bent on doing what they could to hold on to their dominance over large portions of the internet.

The four companies, which have a combined value of $5 trillion, were likened to the robber barons of the early 20th century by the committee. 

"To put it simply, companies that once were scrappy, underdog startups that challenged the status quo have become the kinds of monopolies we last saw in the era of oil barons and railroad tycoons," the report said.

The strongly worded report said that the companies had used their "gatekeeper" position in the digital market abusively to undermine rival companies. 

"By controlling the infrastructure of the digital age, they have surveilled other businesses to identify potential rivals, and have ultimately bought out, copied, or cut off their competitive threats. And, finally, these firms have abused their role as intermediaries to further entrench and expand their dominance.

"Whether through self-preferencing, predatory pricing, or exclusionary conduct, the dominant platforms have exploited their power in order to become even more dominant."

It says that this dominance results in "less innovation, fewer choices for consumers, and a weakened democracy."

The report also says that the social media firms have "too much power, and that power must be reined in and subject to appropriate oversight and enforcement."

It added that the US economy and democracy "are at stake".