Vodafone, one of Britain's largest companies, has warned it could relocate its head office outside the UK following the referendum.
Their warning depends on whether negotiations for a post-Brexit Britain do not offer "freedom of movement" for people, capital and goods.
In a statement, the company said: "The UK's membership of the European Union has been an important factor in the growth of a company such as Vodafone.
"Freedom of movement of people, capital and goods are integral to the operation of any pan-European business."
Vodafone said their European business last year accounted for 55% of their profits, whilst the UK counted for just 11%.
The company, who have 108,000 employees and 462 million customers, added the uncertainty caused by the Brexit result means "it is not yet possible to draw any firm conclusions regarding the long-term location for the headquarters of the Group."
Vodafone will "continue to evaluate the situation and will take whatever decisions are appropriate in the interests of our customers, shareholders and employees".
If any potential move was made, they said it would affect the company's Group HQ in Paddington, west London, and not their office in Newbury.