The southern Indian state of Kerala on Tuesday became the first to legally challenge a new citizenship law that has triggered nationwide demonstrations.

In a petition to the Supreme Court, the state government said the law violates the secular nature of India's Constitution, and accused the government of dividing the nation along communal lines.

The citizenship law backed by Prime Minister Narendra Modi’s Hindu-nationalist party provides a path to naturalization for people from Bangladesh, Afghanistan and Pakistan, unless they’re Muslim. It has triggered nationwide protests and clashes with police, leading to 23 deaths.
The rallies have slowly morphed into much wider anti-government protests.

Critics say the law, which was passed by Parliament on Dec. 11, will be used in conjunction with a citizenship registry that could require all Indians to produce documents proving their origins, a challenge in a country where many people lack official records including birth certificates.

Kerala, a state ruled by a communist party, has strongly opposed the law and passed a resolution against in early January. The state government criticized the law in front-page advertisements in at least three national newspapers on Jan. 10, saying the state is "leading the efforts to protect constitutional values.”

Modi’s Bharatiya Janata Party said the move by the state was political.

Pinarayi Vijayan, chief minister of the state, has also written to the heads of 11 other states not ruled by Modi’s party, urging them to unite in their fight against the law.