The FTSE 100 company, along with unions representing tens of thousands of its workers, will sign off on a joint memo explaining the rationale behind their support of the EU.
"We believe very strongly at BT that it’s important that business puts forward its perspective on the economic risks and realities and advantages - or the other way round - of the EU, so we together with the two main unions are writing to our employees only to explain the position we’ve taken in public around the importance of the EU to the economy of the UK, and directly and indirectly to BT," Sir Mike Rake, BT chairman, told City A.M.
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It is understood that Rake, as well as Gavin Patterson, BT's chief executive, Andy Kerr, deputy general secretary of the Communications Workers Union and Ben Marshall, national secretary for the communications, media and digital sector at Prospect, will put their name to the memo.
The memo is not to tell BT's staff how to vote, but highlight areas of concern around what Brexit would mean, Sky News first reported.
"It goes by definition that virtually all economists - including Leave economists - believe that leaving the EU will create an economic shock that’s going to take some years to recover from. I think there’s no doubt that everyone in the UK in one way or another will suffer from the economic realities of an exit and because of the long period of uncertainty of a renegotiation of whatever trade treaties that might have to be negotiated," Rake added.
"And unfortunately that means the weakest in society will suffer the most."
The memo will also draw attention to a potentially detrimental impact on investment, warn of a drop in the value of sterling and highlight the higher cost of consumer goods and imports.
"Business has an absolute right and obligation to speak out on matters that could have such a significant impact on their businesses. In the context of the referendum, particularly when the facts are not often being properly put across," Rake continued.
The BT chairman also pointed out that BT benefits from the free movement of people across Europe, including the freedom to move people at senior levels, as well as pointing out the benefits of free trade, given near 20 per cent of BT's revenues are made outside of the UK.
Unions including Unite, Unison and GMB have come out in support of the EU, grounded in a belief that workers' rights have benefitted from the UK's membership, another factor that is expected to be included in the memo.