Last week, Narendra Modi was at the top of his diplomacy game.

Travelling halfway across the world and back, the Indian prime minister held hectic negotiations with global leaders with a one-point agenda: winning support for India’s entry into the elite Nuclear Suppliers Group (NSG).

The 48-member NSG, set up after India conducted nuclear tests in 1974, regulates the trade of nuclear technology. While India isn’t a member yet, the group had earlier exempted Asia’s third-largest economy from its restrictions on civilian nuclear trade. India is now lobbying hard to become a member.

Last week, Modi met with the leaders of Mexico and Switzerland—both nations had earlier been skeptical about India’s NSG entry—and managed to convince them. Modi is also pinning his hopes on the US’s ability to garner support from other members.

On Saturday (June 10), he dialled Russian president Vladimir Putin to seek support.

Yet, all his hard work could still go down the drain.

Indications are that China is vehement on blocking India’s entry when its application comes up at Seoul later this month. With its veto power, China can render Modi’s and India’s invigorated campaign impotent.

“When it comes to the accession by non-NPT countries, China maintains that the group should have full discussion before forging consensus and making decisions based on agreement,” a spokesperson for the Chinese foreign ministry said on June 12. “The NPT provides a political and legal foundation for the international non-proliferation regime as a whole.”

Quartz spoke to foreign policy experts to understand why NSG is crucial for India and the reasons for China’s opposition to India’s entry. Here are their responses:

Why is India so adamant on an NSG membership and how does it really help the country?

Toby Dalton, co-director of the nuclear policy program at the Carnegie Endowment for International Peace: Symbolically, India seeks to join the NSG because membership conveys legitimacy as an advanced nuclear state and an ability to participate in international governance and decision-making on nuclear matters. Practically… membership would not bring that many added advantages over the exception to NSG trade rules that India received in 2008. But as a member, India would be able to participate in exchange of information regarding nuclear trade… (This) could be helpful if it (India) chooses to export more dual-use or nuclear-specific technology in the future.

Christine Fair, associate professor at Georgetown University: Access to the NSG will presumably open up the international market for materials which India needs for its domestic nuclear energy program. This, in turn, will free up domestic resources for its weapons program.

Why is Switzerland and Mexico’s support critical for India’s NSG entry?

Michael Kugelman, senior associate for south and southeast Asia at Woodrow Wilson International Centre for Scholars: Any NSG country is critical. India’s plan is to gain the support of every NSG country for its membership, so that China, which resists India’s membership, will feel compelled, in the end, to comply and agree to let India in. Since membership decisions in the NSG are made through consensus and unanimity, India would not be granted membership even if China is the only holdout. This is why New Delhi needs to play an aggressive diplomatic game by gaining the support of every other NSG membership.

Alyssa Ayres, senior fellow at Council on Foreign Relations: The NSG, like the WTO, for example, operates on a consensus basis for decisions. It means that all 48 members need to agree in order to take a decision. So getting Switzerland and Mexico and every other country on board is vital… I would point out here that India, when it refused to ratify the WTO Trade Facilitation Agreement in July 2014, caused the same kind of issue since India broke the required consensus.

But why would China or anybody block India’s entry?

Kugelman: There are various reasons. One is a principled position on non-proliferation—the view that any country that has not formally renounced nuclear weapons proliferation should not be let in. India has not signed the Non-Proliferation Treaty.

The other reason, which really applies only to China, is that letting India in would have deleterious geopolitical impacts. Specifically, for China, letting in India would mean its chief strategic rival would be on an equal footing in this prestigious club. Even more significantly… if India were to gain membership, Pakistan—China’s ally, which has also applied for membership—would be shut out from the club entirely, because India would reject Pakistan’s application.

Dalton: As I understand it, several states believe that because India does not meet one of the principal “factors” that is considered in evaluating a state’s application to join the NSG (that factor being membership in the NPT). India should have to take other steps to reinforce its nonproliferation commitments… For instance, all other states with nuclear weapons that are members of NSG have signed the Comprehensive Test Ban Treaty—India has not. All other NSG members have made a legally binding commitment to disarmament—India has not. India (and the US) have argued that India deserves admission on the strength of its existing commitments and policies. Other states want it (India) to do more…

If India does get into NSG, what role would the Indian prime minister have played in that?

Ayres: Indian diplomacy on this front has been ongoing since the beginning of the civil nuclear agreement. And the US has been stating its support publicly for years now (look at all the joint statements going back several years). But I would say that PM Modi’s stepped up efforts help to clarify the importance India places on NSG membership.

Fair: This has been an ongoing process. In my view, if India gets in, it will be because of India’s long record of not proliferating… Thus, Modi is the beneficiary of India’s long record. And, I would also say that this is the culmination of much American effort to bring India into the nuclear mainstream. Thus, I do not think any single leader can take credit for this on either the US or Indian side.