A regional political party has threatened to attack stores in Mumbai that place English-language signs more prominently than ones in the local Marathi language or refuse to use Marathi signs.
The threats, which police are taking seriously, are the latest effort by right-wing parties to drum up regional pride in a city often seen as India's most cosmopolitan.
Businesses from McDonald's to mom and pop stores have hastily changed their signs to avoid the wrath of political groups that have a history of violence.
Raj Thackeray, leader of the Maharashtra Reconstruction Party demanding the language changes, said shopkeepers could display signs in both languages but the Marathi signs had to be bigger.
The deadline for making changes was Thursday, but many retailers and trade groups have resisted the demands.
"People are insulting Marathi pride with smaller signs. We will not back down," Raj Thackeray told cheering workers late Wednesday. "Traders can take this as a warning or a suggestion, it's up to them."
Mumbai, the financial and entertainment capital, attracts migrants from across India who speak scores of languages. English and Hindi are the most commonly spoken, but with state elections looming, regional party leaders are looking to turn the use of Marathi into a political issue.
Thackeray earlier this year called on his followers to beat up migrants from northern India, leading to a wave of attacks against taxi drivers and laborers.
Earlier this week, party activists distributed threatening leaflets and attacked several shops, shattering windows and breaking furniture. Police have arrested more than 100 people in the attacks.
"We will not tolerate violence," said K.L. Prasad, joint police commissioner. "Patrolling has increased in shopping areas to prevent vandalism."
A 1961 law made it mandatory for stores to display the local script, but many stores have small Marathi signs that are dwarfed by English ones.
Another regional party, the Shiv Sena, recently made it mandatory for official documents to be written in Marathi, not English. The Shiv Sena has repeatedly threatened to attack institutions that failed to replace the city's old name of 'Bombay' with Mumbai. They considered Bombay to be colonially tainted - it was a Portuguese derivation of "beautiful bay" - while Mumbai was taken from the Marathi name for a Hindu goddess.
But in many parts of Mumbai, English signs crowd out Marathi, and some shopkeepers refuse to change.
"We respect Marathi but why should we be forced to make big Marathi signs?" said Viren Shah, a clothing store owner. "Why should our businesses be attacked?"