The holiday is synonymous with International Workers’ Day and May Day in many countries.

In India
The first May Day celebration in India was organised in Madras (now Chennai) by the Labour Kisan Party of Hindustan on 1 May 1923. This was also the first time the red flag was used in India] The party leader Singaravelu Chettiar made arrangements to celebrate May Day in two places in 1923. One meeting was held at the beach opposite to the Madras High Court; the other meeting was held at the Triplicane beach. The Hindu newspaper, published from Madras reported,

    The Labour Kisan party has introduced May Day celebrations in Madras. Comrade Singaravelar presided over the meeting. A resolution was passed stating that the government should declare May Day as a holiday. The president of the party explained the non-violent principles of the party. There was a request for financial aid. It was emphasized that workers of the world must unite to achieve independence
May Day is a National holiday in the country. The holiday is tied to labour movements for communist and socialist political parties. Labour Day is known as "Kamgar Din" in Hindi, "Kamgar Divas" in Marathi and "Uzhaipalar Dinam" in Tamil. In North India, Labour Day is mostly not given its previous importance as a holiday now.

1 May is also celebrated as "Maharashtra Day"and "Gujarat Day" to mark the date in 1960, when the two western states attained statehood after the erstwhile Bombay State was divided on linguistic lines. Maharashtra Day is held at Shivaji Park in central Mumbai. Schools and offices in Maharashtra remain closed on 1 May. A similar parade is held to celebrate Gujarat Day in Gandhinaga

1. The Holiday Celebrates the Achievements of Workers

Indian labourers carry sacks of wheat at a grain market on April 30, 2015, the eve of Labour Day.

The holiday celebrates the achievements of workers around the world. It is celebrated on May 1 in most countries around the world.
The day has also been used by labor unions, socialists and other radicals to call attention to workers’ rights and call for change.

May 1, 2015 is May Day and also International Workers' Day. This holiday was once a pagan celebration of flowers and later became designated to worker's rights.

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2. It Is Closely Linked to Labor Unions & Was First Celebrated in the 1880s

A Labour Day demonstration on May 1, 1926. (Getty)

The holiday was first celebrated in the 1880s, according to a history of Labour Day posted on the Industrial Workers of the World website.
It is on May 1 to commemorate the May 1886 Haymarket Affair, which occurred in Chicago.
From May 1st to May 3rd 1886, 250,000 Chicago-area workers hit the streets to protest long working hours and call for factories to limit days to 8 hours. On May 3, police fired on the peaceful crowd and killed two workers. The rally was held the next day to protest police brutality. At about 10:30 a.m., a police line moved toward the rally and someone threw a bomb at the police, killing one and wounding six others. Police then opened fire and killed four workers, injuring several others.
The IWW says about why the holiday is celebrated:

Truly, history has a lot to teach us about the roots of our radicalism. When we remember that people were shot so we could have the 8-hour day; if we acknowledge that homes with families in them were burned to the ground so we could have Saturday as part of the weekend; when we recall 8-year old victims of industrial accidents who marched in the streets protesting working conditions and child labor only to be beat down by the police and company thugs, we understand that our current condition cannot be taken for granted – people fought for the rights and dignities we enjoy today, and there is still a lot more to fight for. The sacrifices of so many people can not be forgotten or we’ll end up fighting for those same gains all over again. This is why we celebrate May Day.

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3. The Holiday Is Celebrated With Parades & Rallies

A woman displays a placard at speakers corner during a Labour Day protest in Singapore on May 1, 2014. (Getty)

Labour Day has historically been a day for parades, rallies and other celebrations of workers.

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4. Unions & Other Labor Groups Plan to Use the Holiday to Fight For Workers’ Rights

Activists from the Indian Federation of Trade Unions, Communist trade union workers and factory workers hold placards during a protest against state and central government policies that they say negatively impact workers on International Labour Day in New Delhi on May 1, 2014. (Getty)

Many labor groups plan to rally on May 1 to call for worker rights, including better wages and conditions for workers.
Countries like Turkey were bracing for protests on May 1 after clashes between workers and security forces erupted in 2014, according to Al Arabiya. The country has a history of violence on May 1. In 1977, dozens of people were killed during protests at Taksim Square.
Protests are also expected in the United States, which also has a history of clashes between police and demonstrators on May Day. Demonstrations are scheduled in Seattle, Portland and Oakland, and protesters are expected to also continue calls for an end to police violence in the wake of Freddie Gray’s death and several police killings, according to CNN.

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5. Labour Day Is Celebrated on Other Dates in the United States & Other Countries

People hold up signs while listening to U.S. President Barack Obama speak during Laborfest 2014 at Henry Maier Festival Park September 1, 2014 in Milwaukee, Wisconsin. (Getty)

In the United States and Canada, Labour Day is known as Labor Day and is celebrated on the first Monday of September, despite the fact that the original Labour Day originated in Chicago. It traditionally marks the end of summer, along with celebrating workers.