"[I]t is acutely clear from the groundswell of consumer voices over recent months that people are becoming increasingly concerned about the impact of digital on well-being, on democracy - and on truth itself," Weed said. "This is not something that can brushed aside or ignored. Consumers are also demanding platforms which make a positive contribution to society."
Google and Facebook, the two Web companies that dominate online advertising, have come under heightened pressure from lawmakers, academics and industry critics to invest more heavily in filtering out misinformation and abusive content on their networks.
Last year, Google's YouTube faced a backlash from U.S. advertisers who said the company was not doing enough to prevent their ads from being played alongside derogatory and extremist content.
Google has since adopted changes to its YouTube platform, which draws 1.6 billion monthly users. Those changes include stricter criteria for what types of videos can receive ad dollars and more human reviewers of content.
In response to Weed's message, Google said that it takes its partners and users' trust and safety seriously. "We will continue to work to earn that trust every day," the company said.
Facebook chief executive Mark Zuckerberg announced earlier this year that the social network's News Feed would show its 2.1 billion users more posts from their friends and family, as opposed to news organizations and brands, in an effort to generate more "meaningful" interactions.
During Facebook's most recent earnings call, Zuckerberg acknowledged that users spent 50 million hours less per day on the social network than during the previous quarter, in part because they see fewer viral videos - a consequence of Facebook's new push to prioritize the quality of interactions on its platform over the popularity of content.
According to eMarketer's latest estimates, Google and Facebook are expected to claim nearly two-thirds of the U.S. market share for digital ads. Google is expected to command 42 per cent of the market, with Facebook at 23 per cent.
Weed says that 2018 "is either the year of techlash, where the world turns on the tech giants - and we have seen some of this already - or the year of trust, the year where we collectively rebuild trust back in our systems and our society."
Facebook said in a statement, "We fully support Unilever's commitments and are working closely with them."