President Obama is planning as soon as Tuesday to indefinitely block offshore oil and natural gas drilling in parts of the Atlantic and Arctic oceans.

Obama will use a section of the 1953 Outer Continental Shelf Lands Act to implement the protections, Bloomberg and The New York Times reported, citing sources familiar with the plans.

It’s unclear, however, how large Obama’s protected areas will be.

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The action would answer calls from environmentalists to implement so-called 12(a) protections in the Atlantic and Arctic as a more lasting legacy against fossil fuels from Obama.

Obama last month made final a plan for offshore drilling lease sales from 2017 to 2022 that excludes the Atlantic and Arctic.

But that plan’s time period is limited, and President-elect Donald Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE can revise the plan to insert lease sales if he wishes.

Previous presidents have used the 1953 law rarely. In each case, they focused on small areas of water and set time limits in an effort to protect particular species.

It’s unclear how easily Trump can undo the protections, since no previous president has tried to roll back a predecessor’s actions under that law. Congress may also step in to undo Obama’s actions.

Bloomberg reported that Canadian Prime Minister Justin Trudeau might announce similar action to block drilling in Canada’s portion of the Arctic.

The United States’ portion of the Arctic is estimated to have 27 billion barrels of oil and 132 trillion cubic feet of natural gas. The Atlantic has not had testing for oil and gas with modern technology.

The United States’ offshore drilling industry is based almost entirely in the Gulf of Mexico, with limited production off California’s coast.

The oil and gas industry has been pushing the federal government for years to open more areas at least to exploration, with limited success.

The Atlantic does not currently have any offshore drilling. The Arctic does not have any drilling that is in federal waters with traditional, mobile drilling rigs.