The boss of the Australian bus company Greyhound has warned its workers they could be caught “in the crossfire” after signing a contract to help build the Adani coal project in Queensland.

The email from the chief executive, Alex de Waal, seen by Guardian Australia, asked staff not to “undermine your colleagues or brand” by sharing internal updates or posting to social media.

Before the 6 January email, Greyhound had not been linked to the Adani project and the company told Guardian Australia it had not been targeted by protesters.

The email revealed the company, which has more than 600 staff, had won a three-month contract “with an opportunity for extension” with the construction firm BMD, which is building the mine’s railway from the Galilee Basin to Abbot Point.

“The project may create concerns to individual team members in light of the international political, environmental, social and economic debate about climate change underway in the media,” the message read.

Greyhound is a widely recognised Australian brand that says it carries 5 million passengers more than 38m kilometres a year. The company actively promotes bus travel as a less emissions intensive alternative to flying and driving private cars.

Construction work has begun on the Indian-owned Adani mine – one of the most controversial fossil fuel projects in Australia’s history, which will extract coal for export to power stations.

“Servicing BMD is not Greyhound taking a stand on climate change or any other important environmental topic facing our nation and the world,” the email said.

“Greyhound could become one of many companies in the crossfire of the anti-Adani campaign,” De Waal said in the email. “Thank you for being courageous in servicing the regions and customers that mean so much to our business.”

Staff in Townsville, Emerald, Clermont, Belyando Crossing and Mackay would “play a role” in transferring workers, the email said.

“You are entitled to your views and we respect them,” it said.

Employees were asked to “utilise the internal communication channels rather than discussing sensitive business matters with external parties”.

In a Q&A section of the email, the company told staff it had “decided to be courageous” in taking the contract.

Instructions were provided to staff “if you are approached by media or protestors”, asking them to “stay calm”, to refer people to Greyhound’s head office, and then to “walk away and go to a place of safety” before contacting a manager “immediately”.

Defending the company’s environmental credentials, the email said the company wanted to “transition to electric vehicles on reef routes”.

The email noted that De Waal is the chairman of the Citizens of the Great Barrier Reef Foundation, a conservation group led by Andy Ridley, a co-founder of Earth Hour, and promoted by Alan Jones at its launch in 2016. Ridley joined as chief executive in 2017 and relaunched the project with “the climate crisis as a focus”.

The email said the company was the foundation’s “eco-friendly travel partner” and more than $40,000 had been raised for the foundation by offering customers the option of an extra dollar cost on their tickets.

Ridley told Guardian Australia the foundation was “not aware” of Greyhound’s contract with BMD.

He said: “We have a clear ethical charter and for Citizens of the Great Barrier Reef – it’s critically important that we follow that charter. I need to look and check this immediately.”

Guardian Australia has also seen a report prepared by a public relations company advising Greyhound on how it should handle its association with BMD and the Adani mine.

The report included the text of the email written by De Waal, saying “Greyhound Australia must be conscious this update could be forwarded to activists and the media”.

The company’s messages should have “three pillars” that refer to supporting local employment, “delivering environmentally friendly and safe services” and “supporting regional communities”, the report said.

Several major companies associated with the controversial coalmine have been targeted by campaigners.

Billie Tristram, 14, is a climate change campaigner who has helped organise school strike marches in Townsville.

“We travel to school camps using Greyhound buses – a lot of schools use them. [Greyhound] is putting economics first instead of the environment. It’s like a slap in the face. I won’t be travelling with them until they back out.”

In January, the German technology company Siemens said it would honour its Adani contract after carrying out a review.

In December, the engineering firm GHD ended a 10-year association with Adani after that company was also targeted by campaigners.

Julien Vincent, the executive director of Market Forces, a group that tracks the relationships between corporations and fossil fuel industries, said Greyhound was now being placed on its “Adani list” of contractors associated with the mine.

He said the company’s email suggested it was aware of the “reputational risk” of being associated with the project.

“This is not to let any other fossil fuel projects off the hook, but we are drawing a line in the sand [on Adani].”

In a statement, Greyhound verified the email and its contents, and said its Greyhound Resources business had been operating for more than 10 years in Queensland’s Bowen basin and in Gladstone.

“Greyhound’s work in the resources sector reduces companies’ overall carbon footprint,” the statement said.

The company said it had not yet been targeted by anti-Adani campaigners.

“We want our team to be safe and secure while delivering a transport solution that takes light vehicles off the road and provides safe transfers for workers from towns and cities to camps and site.”

Asked if the company anticipated criticism from young people who used their services, the statement said: “All generations can make appropriate ethical choices in contributing to lessoning their carbon footprint on this planet.

“Greyhound is not only a comfortable and scenic way to travel, it is the most carbon efficient per person for long distances. We have younger customers choosing bus as a greener way to travel over planes, trains and automobiles.”