Support for a global pact banning nuclear weapons is growing within NATO, an advocacy group says.

As President Biden and his NATO counterparts focus on nuclear-armed Russia at their summit meeting on Monday, they may also face a different sort of challenge: growing support, or at least openness, within their own constituencies for the global treaty that bans nuclear weapons.

The International Campaign to Abolish Nuclear Weapons, the Geneva-based group that was awarded the 2017 Nobel Peace Prize for its work to achieve the treaty, said in a report released on Thursday that it had seen increased backing for the accord among voters and lawmakers in NATO’s 30 countries, as reflected in public opinion polls, parliamentary resolutions, political party declarations and statements from past leaders.

The treaty, negotiated at the United Nations in 2017, took effect early this year, three months after the 50th ratification. It has the force of international law even though the treaty is not binding for countries that decline to join.

The accord outlaws the use, testing, development, production, possession and transfer of nuclear weapons and stationing them in a different country. It also outlines procedures for destroying stockpiles and enforcing its provisions.

The negotiations were boycotted by the United States and the world’s eight other nuclear-armed states — Britain, China, France, India, Israel, North Korea, Pakistan and Russia — which have all said they will not join the treaty, describing it as misguided and naïve. And no NATO member has joined the treaty.

Nonetheless, an American-led effort begun under the Trump administration to dissuade other countries from joining has not reversed the treaty’s increased acceptance.

“The growing tide of political support for the new U.N. treaty in many NATO states, and the mounting public pressure for action, suggests that it is only a matter of time before one or more of these states take steps toward joining,” said Tim Wright, the treaty coordinator of the International Campaign to Abolish Nuclear Weapons who was an author of the report.

Timed a few days before the NATO meeting in Brussels, the report enumerated what it described as important signals of support or sympathy for the treaty among members in the past few years.

In Belgium, the government formed a committee to explore how the treaty could “give new impetus” to disarmament. In France, a parliamentary committee asked the government to “mitigate its criticism” of the treaty. In Italy, Parliament asked the government “to explore the possibility” of signing the treaty. And in Spain, the government made a political pledge to sign the treaty at some point.

Nicola Sturgeon, the leader of Scotland, where some British nuclear weapons are stored, said in January that if Scotland declared independence, her government “would be a keen signatory, and I hope the day we can do that is not far-off.”

There is nothing to prevent a NATO country from signing the treaty. But the bloc’s solidarity in opposing the accord appears to have weakened, emboldening disarmament advocates.

Promoters of the treaty have repeatedly said they do not expect to see nuclear-armed countries join anytime soon. Rather, they have said the treaty’s increased acceptance by other countries will create a shaming effect, similar to how treaties that banned chemical weapons, land mines and cluster munitions have drastically cut their use and stigmatized violators.