BT’s 80,000 staff have been told that company bosses and union leaders back remaining in a reformed EU.

The joint message, sent on Monday by the telecoms giant’s chairman and chief executive and leaders of the Prospect and CWU unions, does not tell them how to vote, saying that “is of course a matter for each individual to decide”.

But the letter, which was immediately dismissed by Leave campaigners, does state that “the majority of businesses – large, medium and small – believe we are better off staying in”.

The letter says: “The vote is so important that we, supported by the BT board, believe we have an obligation to write to you to explain our views.

“The leadership of the Communication Workers Union and of the Prospect Union here at BT both agree, and so we are issuing this joint message.

“We want to give our view on the potential impact that next week’s decision may have on the company and on its current, past and future employees.

“Firstly: the vote will have an impact on the economy, and knock-on effects on companies operating in the UK.

“That includes us at BT, and it is one of the reasons we favour the UK remaining inside a reformed EU.

“We are far from alone: you will have seen that the majority of businesses – large, medium and small – believe we are better off staying in.

“The nation has already seen a slowdown in investment and economic activity because of uncertainty over the outcome of this referendum.

“The value of the pound has also been affected, something which would, in the view of many, be exacerbated in the event of the UK leaving the EU. The pound’s value internationally affects the cost of everything from holidays to imported goods.

“Virtually all major independent experts believe leaving the EU would result in an economic downturn, one from which it may take several years to recover. This will, of course, affect us at BT.

“Secondly: as many of you will know, we at BT earn about a fifth of our revenues outside the UK. It is the European Union which helps us to export.

“It guarantees we face minimal import taxes or other trade barriers when we provide communications services and IT support to our customers across the EU’s 28 member states.

“And it does the same beyond Europe, negotiating deals that open markets to us across the world, on terms it would be difficult for the UK alone to replicate.

“Many in BT, especially in the Global Services division, can easily travel across Europe, so that they can work with talented colleagues throughout the continent. Exiting the EU could make it harder to do so in future.

“Finally: the EU has been a progressive force in the workplace. It helps to underpin essential rights for workers and to prevent any unjustified ‘levelling down’ of employment laws.

“Whatever your point of view, we would encourage you to vote on this important issue.”

The letter was sent by BT chairman Sir Mike Rake, chief executive Gavin Patterson, CWU deputy general secretary Andy Kerr and Ben Marshall, who is national secretary for the comms, media and digital sector with the union Prospect.

However, Matthew Elliott, chief executive of Vote Leave, said: “Everyone knows that renegotiation was an utter failure that achieved nothing.

“If we really want to take back control of our economy, our democracy and our borders then we have to Vote Leave.”