LONDON (Reuters) - European planemaker Airbus Group (>> Airbus Group) said its future investment in Britain could depend on whether the country remains in the European Union, in a warning to its British employees ahead of a vote on June 23.

The economic impact of a 'Brexit' is one of the key issues for voters ahead of a referendum on Britain's EU membership. As the vote nears, some companies are becoming increasingly vocal on the potential impact of a vote to leave.

Airbus wrote to employees on Monday to warn of the consequences of leaving.

"We all need to keep in the back of our minds that future investments depend very much on the economic environment in which the company operates," the letter signed by Airbus's chief operating officer Tom Williams and its UK head Paul Kahn said.

It has already said it believes its British operations are more competitive because they are within the 28-member bloc.

Airbus's letter to its employees followed one sent by German carmaker BMW in March which also set out the risks the company would face if the country voted to leave.

France-based Airbus said in its letter that its business model is based on its ability to freely move products, people and ideas around Europe.

The bosses at more than a third of Britain's biggest companies including major oil firms Shell and BP (>> BP plc) and its largest telecoms group BT (>> BT Group plc) warned in February that leaving the EU would put jobs and investments at risk.

Some companies do, however, favor an exit from the EU. The campaign for Britain to leave the bloc has been backed by 250 business leaders including the former chief executive of HSBC, the Vote Leave group said in March.

(Reporting by Sarah Young; editing by Kate Holton)

Stocks treated in this article : Airbus Group, BT Group plc, BP plc