The U.N. Arms Trade Treaty (ATT) opens for signature on June 3. Well over 30 nations will sign it immediately, and the U.S. has announced it will follow suit.

Once 50 signatories ratify the treaty, implementation begins 90 days later. And implementation will present new risks to the U.S.

U.S. Assistant Secretary of State Tom Countryman insists implementation will bring “no change in legislation, policy, or procedures.” That promise will be nearly impossible to keep, since key terms in the treaty have no fixed meaning. As they evolve, the U.S. will change its policies accordingly.

But the ATT was never designed to stand on its own. It will be fleshed out in innumerable ways. That process that will end up determining what the treaty actually means.

For all the concerns expressed about the text of the treaty, it is how the treaty is implemented that matters.

Even treaty advocate Countryman acknowledges the text is “ambiguous.” For the treaty’s backers, that’s a virtue. It would’ve taken forever to negotiate a well-defined treaty governing all of international arms trade. Lack of clarity was expedient. But it’s also why the implementation phase brings new risks.

Governments around the world – including the U.S. – will offer “implementation recommendations.” Left-wing non-governmental organizations (NGOs) that were instrumental in treaty negotiations will pressure corporations to adopt their “best practice guidelines” and nations to draw upon their “model legislation.” And corporations will adopt “voluntary codes of conduct” to defend themselves.

The U.S. likes to conduct serious international business through treaties. But the left, not so much.

Treaties are based on national sovereignty, which the left resents. They often require consensus among the negotiating nations, which – as the left sees it – allows the U.S. to block the advance of global progressivism. And they need Senate approval, which again limits the power of the left.

The new strategy is to substitute voluntary agreements for treaties. Such agreements are not all bad.

The U.S.-led Proliferation Security Initiative, which seeks to stop trafficking in weapons of mass destruction, is a voluntary partnership. But all too often, such agreements start off as voluntary and gradually become compulsory.

The private sector is vulnerable to this bait and switch, because companies can be threatened with formal controls if they don’t go along with ever-tighter “voluntary” ones.

The ATT is a hybrid: it’s a treaty, but it will be filled in with voluntary activities that are not easily subject to Congressional oversight. It may resemble the “Voluntary Principles on Security and Human Rights Initiative,” which the State Department defines as “a multi-stakeholder initiative made up of governments, companies, and non-governmental organizations” for mining and oil drilling industries. The Initiative is not legally binding, but it allows the government to put pressure on energy companies.

Left-wing NGOs have pioneered another approach in Europe. There, nations that signed the Convention on Cluster Munitions have come under NGO pressure to ban investment in any firm associated with the manufacture of cluster munitions, even though the Convention does not require this. Applied to the ATT, this strategy would lead to commercial or financial attacks on U.S. firms that exported in violation of the ATT as interpreted by other nations.

The New York Times is stumping for a third approach. A recent front-page article headlined “Gun Makers Saw No Role in Curbing Improper Sales” implies that firearms manufacturers should take “constructive voluntary action” or face lawsuits.

Though the ATT creates no obvious new path for lawsuits, it does open up the realm of international trade and finance to NGO demands for “constructive voluntary action.”

U.S. businesses will try to get out ahead of the implementation train. They will find it hard to succeed. This is partly because the U.S. export control system is unique, so approaches built here will not reflect legal realities elsewhere.

It’s partly because the U.S. government will never tell them that their voluntary efforts are good enough, and the NGOs will certainly never say so. Since U.S. business always tries to minimize legal and public relations risks, it will be forever chasing an ever-receding voluntary horizon.

But it’s fundamentally because the ATT is not an administrative document. U.S. businesses are used to dealing with a bureaucratic system that, while hideously complex, does have some predictability. The ATT, though, is political. The demand for it was political; its terms are political, and its implementation will thus have to be political.

At heart, many of its backers abroad – and some in the U.S. – dislike the entire arms trade and the U.S. predominance in it, as well as the Second Amendment. That means that, as the treaty moves from signature to implementation, the risks it poses are only going to get worse.