The organisation's report into corporate political engagement, published today, included assessments of UK companies’ political contributions and lobbying, as well as the so-called revolving door between corporations and politics.
Transparency International’s findings ranked major tech firms among the lowest across these categories.
Amazon and Facebook received the lowest ranking for “responsible lobbying”, indicating they have few or no clear policies on how they influence political decision-makers.
Amazon also ranked among the worst companies for political contributions, suggesting the company is not doing enough to disclose its global political spending.
The report looked at the so-called revolving door between corporate roles and political positions, including so-called cooling-off periods enforced on former public officials.
Google ranked lowest in this category, with the report saying a lack of transparency in this area leaves the public sector exposed to potential conflicts of interest.
Google recently hired David Cameron’s former adviser, Tim Chatwin, as its new head of EMEA communications.
Facebook appointed former deputy prime minister Nick Clegg as head of its global affairs team in October.
“The findings of our 2018 index are definitely a cause for concern,” said Kathryn Higgs, director of the Transparency International UK business integrity programme.
“Businesses must be far more transparent in how they engage with politicians or they risk damaging their reputations with the public and in the long-run will themselves lose out.”
The report comes amid a growing lobbying presence in UK tech firms. In the last two years Google, Amazon and Facebook have doubled the number of policy specialists they employ, according to the Daily Telegraph.
But the tech companies were not alone in scoring low results in the report, which found four in five firms had poor standards.
Overall, Amazon and Facebook received the average ranking, while Google scored slightly higher.
Amazon declined to comment on the report. Facebook and Google have been contacted for comment.