Others say substitutes like soya or beans, suggested by an Iskcon official, are not widely consumed in the state and may not be easily accepted by students.

Some politicians and activists have proposed a middle path: letting students choose between eggs and a vegetarian alternative.

Eggs have long been considered one of the cheapest and most efficient sources of high-quality protein. They usually cost around eight rupees ($0.08; £0.06) each and have been part of Bengal’s food culture for generations.

Defending the decision, Chief Minister Suvendu Adhikari said the project was aimed at providing students with “good and pure food”.

“You don’t have to say Hare Krishna [the movement’s devotional chant]. “No one will force you,” he said, rejecting criticism that the move was driven by the BJP’s Hindu nationalist ideology.

Iskcon says the criticism is misplaced. Through the Akshaya Patra Foundation, which he founded, he provides school meals to around one million students in 16 states, including Karnataka, Andhra Pradesh, Gujarat and parts of Delhi.

Radharaman Das, vice-president of Iskcon in Kolkata until last week, told local media that the organization takes special care to ensure its meals are nutritious and hygienic.

He said the vegetarian menu would provide enough protein and vitamins to match the nutritional value of eggs.

Das has since been removed from his organizational positions, although Iskcon has not publicly explained the decision.

The BBC has contacted Iskcon for further comment.

The dispute has also renewed attention on India’s school feeding plan.

Launched nationwide in 1995 and rooted in a school feeding program started in Madras (now Chennai) in 1925, it has grown to become one of the largest in the world, serving more than 110 million children.

The federal government sets calorie and protein goals, but states decide how to achieve them. As a result, there is no single national menu and meals vary throughout the country.

In Bihar, children are often served rice with legumes or chickpeas, plus an egg once a week. In Tamil Nadu, school lunches usually include rice, sambar (lentil and vegetable stew), vegetables and eggs.

Other states only serve vegetarian meals. In Gujarat, Uttar Pradesh and Delhi, menus often include rice or wheat-based dishes with legumes and vegetables, sometimes accompanied by milk, paneer (cottage cheese) or fruit.

The way meals are prepared also varies.

In many public schools, dedicated staff cook them on site. Elsewhere, state governments contract with nonprofit organizations to prepare and distribute meals that meet prescribed nutritional standards and state menus.

For almost a decade, students in Kolkata’s public schools have been served an egg on some days of the week, along with rice, pulses and vegetables. Now, that could change.