The architects of Plan S are unlikely to back away from strict and rapidly approaching deadlines for a “big flip” to open access publishing despite mounting pressure for a longer transition period, Times Higher Education understands.

More than 900 responses to the proposed rules, under which participating funders would require all the research that they had supported to be made freely available at the point of publication from next January, were submitted by universities, societies and publishers during a three-month consultation that ended earlier this month.

Although many respondents support the principles of the project, there is concern that not enough time has been allowed for compliance with the proposed rules.

Plan S has so far won the support of 14 European national funders, the European Commission and three charitable funders, including the Wellcome Trust and the Bill & Melinda Gates Foundation. Researchers supported by those organisations will, in effect, be barred from publishing their work on platforms that do not support immediate open access. This would outlaw publication via a green open access model under which articles are made freely available after an embargo period.

There will be a three-year transition period allowing publication in “hybrid” journals that currently offer a mix of subscription-only and open access papers, providing that they have made a commitment to switch to full open access.

The League of European Research Universities said that its members felt that the “timescales which underpin Plan S are very challenging” and “should be lengthened accordingly”. UCL – the institution behind the UK’s first open access university press – urged a “wholesale rethink of the strategy and timelines for moving to 100 per cent open access”. The transition “should be measured in years, not weeks”, UCL said.

Paul Ayris, UCL’s pro vice-provost for library services, said that the “time frame…is clearly an important issue, and it is common in responses to Plan S to find that the submitter is suggesting that a longer time frame is required”.

A major sticking point was that some bigger deals with major publishers are negotiated for five-year periods, meaning that legally binding subscription contracts that did not comply with Plan S would remain in place long after the deadline passed.

“Universities have dozens and dozens of ‘big deals’,” Dr Ayris said. “It would be physically impossible to renegotiate all of them in 10 months.”

However, Plan S leaders have previously stressed that members are not required to apply the open access mandate to pre-existing contracts. The majority of participating funders told THE that they had no plans to do so, although the Wellcome Trust said that its open access policy would apply to existing funding agreements from January onwards.

The outlawing of embargoed green open access is thought to be a major obstacle to widespread adoption of the Plan S principles in North America and Australia.

But THE understands that Plan S leaders are unlikely to back down, regarding “no paywall” as a key principle of the scheme. A source said that “no special allowances” would be made for funders or participants even in countries where a zero embargo period was perceived to be problematic.

rachael.pells@timeshighereducation.com