The Indian manufacturing giant Tata is suing Greenpeace India over a computer game it has created to publicise the alleged impact on turtles from the company's development of a new port.

The Pac-Man-style game is defamatory and an abuse of copyright, Tata Sons, Tata companies' bulk shareholder, said on Friday at the New Delhi high court. The court has served notice to Greenpeace, which has until 12 August to respond in writing to the lawsuit.

Greenpeace India launched the game at the start of June, the latest step in its seven-year campaign against Dhamra port, which is due to open this summer at Bhadrak in Orissa, a state on India's eastern coast. The environmental group alleges that the development will endanger local turtles. Turtle Vs. Tata, which is still live online and has been played by nearly 25,000 people, places a turtle in the role of Pac-Man battling against Tata logos in the place of ghosts.

Tata is a huge international conglomerate with revenues of $70.8bn in 2008-09. It owns Jaguar Land Rover and the steel company Corus in the UK.

In a statement, a spokesperson for the company said: "Greenpeace has unauthorisedly used the trademark Tata as well as the 'T within a circle' device without the permission of Tata Sons, thereby infringing the trademark rights of Tata Sons. Greenpeace herein has not only infringed the trademark rights of Tata Sons, but is also maligning the reputation of Tata Sons."

Areeba Hamid, oceans campaigner at Greenpeace India, told the Guardian the case had no merit either on grounds of copyright infringement or defamation. She added they will not change the game unless the court directs them to.

Ashish Fernandes, oceans campaigner for Greenpeace India, said: "This is a desperate attempt to stifle the growing criticism over their port project, and divert attention from the real issue of the impact it will have on a biodiversity-rich area. Public opinion is on the side of the turtles – over 150,000 Indians, leading scientists and turtle biologists, politicians and national NGOs have come out against the port. By first ignoring and now trying to silence these voices, Tata has shown that it cares only about its bottom line, and not the environment."

Tata Steel is jointly developing the new port in a 50:50 project with L&T, another Indian conglomerate. The port development team have previously said the port is not in the turtles' nesting zone or where they congregate for mating, and says it has worked with the International Union for Conservation of Nature to identify potential areas of damage.

Greenpeace has been campaigning against the port since 2003. The group says the developers' environmental impact assessment report was flawed. It describes the site as "ecologically sensitive", noting that it is 5km from India's second largest mangrove forest, the Bhitarkanika Sanctuary, and less than 15km from Gahirmatha nesting beaches, the world's largest mass nesting site for Olive Ridley turtles. Hamid added the NGOS was also concerned about a white-bellied snake and a frog that a 2007 Greenpeace assessment of the site found were the first recorded instances of the species on the Indian mainland. The case begins tomorrow.

• This article was updated on 27 July. The second paragraph originally said "Greenpeace has until tomorrow to respond to the lawsuit" - the court has now indicated Greenpeace must reply by 12 August.