Police in northern India used drones to fire tear gas at thousands of protesting farmers.

The farmers and their supporters were marching to New Dehli on Tuesday to demand guaranteed minimum prices for crops. 

Security in India’s capital was tightened, and halfway through the day, police fired the gas. The marchers were dispersed at a border crossing between Punjab and Haryana states, about 143 miles north of New Delhi.

The march is the latest in a series of protests in India which began more than two years ago. It comes months ahead of the country’s national elections in which Prime Minister Narendra Modi will seek a third term. 

Farm unions, an influential voting bloc, are seeking guarantees backed by law to provide more state support or buy crops at a minimum price. They also want the government to honour a promise to double their income.