WASHINGTON -- As tensions between NATO and Russia intensify amid growing fears of confrontation, US lawmakers are raising questions over the relationship between the United States and the military alliance.

That is the issue at the center of a new bipartisanbillled by Democratic lawmaker Jimmy Panetta and his Republican counterpart Joe Wilson.

TheNATO Shield Actwould require congressional approval before a president could initiate a US withdrawal from NATO.

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Panetta, in an interview with RFE/RL on October 1, argued that the measure is particularly important at a moment when Russia is testing the alliance and uncertainty surrounds Washington's future force posture in Europe.

The legislation, introduced September 24, would require the president to consult Congress within 72 hours of considering a withdrawal from the military alliance and submit a report explaining the legal basis, strategic rationale, and expected consequences.

Any withdrawal action would end after 30 days unless Congress approved it.

Panetta said NATO is one of the most consequential and successful security alliances in the history of the world and argued that any fundamental change in US national security policy should not be left to the president to decide.

But his argument goes beyond the possibility of a formal US withdrawal.

Panetta said Russian President Vladimir Putin is already testing NATO through pressure, probing, and poking at the alliance before any potential move toward direct confrontation.

He pointed to Russia's activities around the Baltic region, Poland, and other NATO border states as examples of what he described as gray-zone warfare.

For Panetta, the danger lies partly in actions that remain below the threshold of open war.

We cannot let gray-zone warfare go unnoticed and unresponded to, he said, warning that Russia could gradually pressure NATO members in much the same way China has applied pressure around Taiwan.

An attack on one of us will be an attack on all, Panetta said, invoking the alliance's collective-defense principle laid out in Article 5 in NATO's founding treaty.