A member of Greenpeace International, Aaron Gray-Block, was "barred" from entering India despite having a valid business visa and necessary documents, the NGO said on Monday.
The organisation has demanded an explanation from the ministry of home affairs.
Gray-Block was travelling from Sydney and was not allowed to enter India at the Bengaluru airport on Saturday midnight. His passport was seized and he was put on a flight to Kuala Lumpur.
"His passport was returned to him after he landed in Kuala Lumpur. He is now back in Australia. This is not the first time Greenpeace staff from other countries have been denied entry into India," a Greenpeace statement said.
"No formal reason was given by the immigration officials for the decision and he was not officially deported," the statement said.
He was travelling to India on an Australian passport to take part in a series of meetings with staff and to learn more about Greenpeace India's current campaigns, it added.
Seeking a "full explanation" from the home ministry, Divya Raghunandan, Greenpeace India programme director, said: "Our colleague has a valid business visa, and yet he was prevented from entering India with no reason given.
"We support the free movement of people across the world, which is crucial to the work of business as well as charities. Greenpeace International is a global organisation that helps to find solutions to environmental problems. There is absolutely no reason why one of its staff members should be treated in such an arbitrary way.
"We are forced to wonder if all international staff of Greenpeace will now be prevented from entering the country? If Home Minister Rajnath Singh has a stand on this, then we would like him to state it clearly," said Raghunandan.
Greenpeace India activist Priya Pillai was stopped from flying to London in January. However, on March 12, Pillai was granted relief by the Delhi High court which quashed the look out circular issued against her.
On April 9, Home Minister Rajnath Singh blocked Greenpeace India's bank accounts for which the environmental group had to seek interim relief from the Delhi High Court.
However, on May 27 the Delhi High Court allowed NGO Greenpeace India to operate two of its domestic accounts, which were frozen by the central government.
