NEW DELHI, April 9 -- Weeks before India heads into a two-month-long election with nearly a billion voters, political party merchandise and flag makers are expanding operations and working overtime to meet a surge in demand.

Ahead of the first voting day of the seven-phase election on April 19, garment makers are temporarily converting factories where they usually make saris into production hubs for election flags and banners.

One such factory owner, Mukesh Agarwal, said there are as many as 40 similar factories in Mathura, a temple town in Uttar Pradesh, India's largest state and a key political battleground.

"The cheapest and best items used for political campaigns are banners and flags," Agarwal said.

Election merchandise is a low-ma...