NEW DELHI — The passage of India's new citizenship law has sparked protests nationwide this week in a major display of opposition to Prime Minister Narendra Modi. A coalition of civil society organizations planned protests in 20 cities Thursday, but authorities in two states and the nation's capital imposed regulations prohibiting public gatherings.

Here's what you need to know about the legislation roiling the world's largest democracy.

What is India’s new citizenship law?

The Citizenship Amendment Act was approved by India’s Parliament on Dec. 11 and makes religion a criterion for nationality in India’s citizenship law for the first time. It creates an expedited path to citizenship for migrants from three countries — Pakistan, Bangladesh and Afghanistan — who illegally entered India by 2014, provided they belong to six religions. The religions are Hinduism, Buddhism, Christianity, Sikhism, Jainism and Zoroastrianism. Notably absent from the list: Islam, the religion practiced by about 200 million of India’s more than 1.3 billion people. 

Why is the law controversial?

The law has sparked backlash on several levels. When India became independent in 1947, its founders sought to create a secular nation where all religions were welcome — in contrast with Pakistan, which was conceived as a home for the subcontinent’s Muslims. By giving preference to certain religions in citizenship law, the government is moving away from that ethos.

The measure is “the first legal articulation that India is, you might say, a homeland for Hindus,” Pratap Bhanu Mehta, one of India’s most prominent political scientists, told The Washington Post.

The law has deepened worries that Modi, who leads the Hindu nationalist Bharatiya Janata Party, is pursuing policies that effectively turn India’s Muslims into second-class citizens. In August, the prime minister stripped India’s only Muslim-majority state — Jammu and Kashmir — of its autonomy and statehood, reversing seven decades of policy. In November, India’s Supreme Court allowed the construction of a grand Hindu temple at the site of a 16th-century mosque illegally destroyed by Hindu extremists.

While some critics of the citizenship law view it as discriminatory and counter to India’s founding principles, for others the opposition to the measure is rooted in different concerns. In India’s northeast — a collection of seven states bordering Bangladesh, China and Myanmar — there are long-standing tensions over migrants entering the region. Residents there worry that the law makes it easier for migrants to become citizens, hastening demographic and linguistic change.

Why does the government say the law is necessary?

The Modi government says the law is a humanitarian measure aimed at helping persecuted religious minorities from three neighboring countries who have entered India. Such communities have faced hardship and, at times, violence in Pakistan, Afghanistan and Bangladesh — all Muslim-majority nations — and the government says India has a moral responsibility to help them.

Opponents say there are several problems with the government’s logic. The first is that the law applies only to migrants who entered India by 2014 and does not help religious minorities living in those countries. The second is that the government has restricted its concern to religious minorities, not members of other types of persecuted communities. Experts say the government could have achieved its stated goal without using language that explicitly excludes Islam.

What has been the reaction so far?

International observers have expressed serious concerns about the measure. The U.S. Commission on International Religious Freedom said the legislation marked a “dangerous turn” and called upon Congress and President Trump to consider sanctions against Amit Shah, Modi’s powerful minister of home affairs. The U.N. High Commissioner for Human Rights said the law was “fundamentally discriminatory” and appears “to undermine the commitment to equality before the law enshrined in India’s constitution.”

In India, the furor shows little sign of ebbing. Days of protests broke out in India’s northeast following the passage of the measure, particularly in Assam, where four people were shot and killed by police. Protests have also taken place in cities and at universities across the country, including in the capital New Delhi, where police stormed the campus of Jamia Millia Islamia University late Sunday. A fresh round of demonstrations broke out this week in response to the actions of the police.

Protests also spread beyond India, with demonstrations taking place in the United States and Britain. More than 10,000 academics issued a statement condemning police brutality against students and calling the citizenship law “discriminatory and unjust.”

What happens next?

Opponents of the measure are preparing to challenge its legality in India’s Supreme Court, but a verdict in the case could take months or longer.

Shah, Modi’s second-in-command, has described the citizenship measure as a first step. The next priority is to implement a nationwide register of citizens in which all Indians could be required to provide documents proving their citizenship. The exercise would be modeled on a registry carried out in Assam, a byzantine process that threatens to leave 2 million people stateless.

Shah says no Indian citizen has anything to fear from a nationwide register of citizens that aims to weed out illegal “infiltrators.” (He has also called such migrants “termites.”) But many Indian Muslims are afraid the exercise is an excuse to target their claims to citizenship — and some have begun to assemble their ancestral documents ahead of a possible registry.