The European Union is set to throw the weight of its €80 billion (£64 billion) research funding programme behind open-access publishing, Times Higher Education has learned.
An official at the European Commission, which is drafting proposals for the Horizon 2020 programme, said that for researchers receiving funding from its programme between 2014 and 2020, open-access publishing "will be the norm".
A pilot under way in seven areas of its current funding programme will be extended to become a mandate across all peer-reviewed research in the new scheme, which will cover fields ranging from particle physics to social science.
The organisation is still negotiating with publishers and working up the details of the proposal, but it plans to put forward further ideas at an event in Brussels on 20 June and to publish an official policy before the summer.
Speaking to THE, the director general of research and innovation at the Commission, Robert-Jan Smits, said its commitment to free online access was essential to driving free movement of researchers and ideas within Europe.
"With our €80 billion we can make one hell of a difference," he said. "We're clear about the huge potential that exists on open access."
Tim Gowers, the University of Cambridge professor of mathematics and Fields medallist who in the UK led a boycott of publisher Elsevier over its perceived opposition to open access, said that the biggest effect would be symbolic.
"I think it will be hugely significant, even just if in getting people to make similar decisions," he said. "It begins to feel as though the snowball is getting bigger."
A number of research funders in the UK have increased their focus on open-access publishing this year. Having Europe join the bandwagon is likely to please David Willetts, the universities and science minister, who in a speech at the Publishers Association earlier this month acknowledged that the UK could lose out financially if it were alone in promoting open access.
The UK government's proposals will be finalised after a working group chaired by Dame Janet Finch reports next month.
But with an annual budget almost 20 times that of the Wellcome Trust, the giant biomedical charity - one of the first big funders to have an open-access mandate - Horizon 2020's policy may have a huge effect on others' decisions.
Although the Commission is keeping the exact requirements under wraps, the pilot that will shape the eventual scheme used both "gold" and "green" models of open access.
During the pilot, the Commission underwrote the costs that publishers charged authors to publish their work freely, known as the "gold" model, but only for the duration of the project.
It also explored the "green" model, in which holders of European Research Council grants were required to make their publications available in open-access repositories within six months of publication, while other grant holders had to do so after six to 12 months.
Stephen Curry, professor of structural biology at Imperial College London and a prominent advocate of open access, welcomed the Commission's move.
But he stressed that real commitment would mean the Commission agreeing to pay publishers' fees even after a grant had ended, or contributing to a central pot of funding within researchers' institutions to pay for open-access publishing.
"It looks to me like the Finch committee is thinking along those lines as well," he said.
The Commission also confirmed that it is in discussions with several publishers about the proposals.
Elsevier refused to comment on the Commission's plans, but it has previously said it is opposed to government mandates on open access.
Writing in response to a blog by Professor Gowers suggesting that the company was trying to influence the Commission, Alicia Wise, Elsevier's director of universal access, insisted that it was lobbying Brussels "to ensure that whatever policy is adopted can be implemented successfully".
"Publishers may not like it, but they're going to have to fall in line," Professor Curry said.
"This is part of a bigger and growing picture. If you see the funders falling into line and adopting consistent policies with each other, that sends a clear signal that this is just the way we do research."