Fishermen could soon be given carte blanche to overfish without needing to worry about restoring fish populations to a healthy state under a leaked European commission proposal seen by the Guardian.

If it is approved, the blueprint for the Baltic Sea could soon be applied to the North Sea too, potentially threatening the future of some cod species, MEPs say.

The plan would add exemptions to catch limits that are supposed to become mandatory by 2020 and practically remove a commitment to restoring fish stocks to healthy levels by the same year.

“With this proposal, overfishing will continue and, in a worst case scenario, [Baltic] cod will disappear. It is that serious,” Linnéa Engström, the vice-chair of the European parliament’s fisheries committee told the Guardian.

“We already know that the Baltic is a vulnerable sea. There are problems with salinity and oxygen levels and some fish stocks are doing very poorly. The scientists don’t know why they are not recovering as they should. They say that some fish stocks are in such a poor state that it is not possible to do a proper evaluation.”

The common fisheries policy, which began in 2014, sets the principle that overfishing must end by 2020, in order to restore and maintain fish stocks at healthy levels. But the new proposal would allow fishing above those levels, conservationists argue.

Catches of some fish in the Baltic Sea would increase well above levels recommended by scientists under the new plan, according to the Pew Charitable Trust.

Western Baltic cod catches would break the current sustainable fishing limit by 60%, while 63% more North Sea sole would be caught than current policy allows.

“This proposal would annihilate the common fisheries policy goal of ending overfishing by 2020,” said Markus Knigge, an advisor to the Pew Trust. “It is of tremendous importance. It is a real breaking point. The commission has already requested similar ranges for fish in the North Sea and northwest waters and if this text is accepted for the Baltic, proposals will follow there too.”

The Trust is calling on the Dutch fisheries minister, Martijn Van Dam, who is leading fisheries ministers on the issue, to secure a deal in line with the policy.

The new plan would replace a current “maximum sustainable yield” of fish that can be caught each year with a flexible formula containing upper and lower ranges. Exemptions to catch levels would be allowed where these could protect fish from harming themselves or each other, and also in “mixed fisheries”.

Lawyers say that the commission plan, which was shared with MEPs on the European parliament’s fisheries committee last Friday, would breach the EU’s current commitments on sustainable fishing.

“The proposal would create ranges for catch limits that put higher pressure on fish stocks than is legally allowed under the common fisheries policy,” said Sandy Luk, an attorney for the green law group ClientEarth.

The commission drew up the proposal after taking soundings from EU countries in the European council. But the European parliament is restive on the issue and has the power to block and amend legislation.

“It is almost at the stage of ‘no plan is better than a really bad plan’,” Engström said. “Of course, this proposal will serve as the blueprint for other plans and that’s why it is so important we get it right.”