BT (BT) Chairman Michael Rake and CEO Gavin Patterson have joined forces with the heads of two of the U.K. telecoms provider's unions in a letter to staff outlining BT's support for remaining in the European Union ahead of the country's referendum on June 23.

BT employs 88,000 employees around the world, with around 72,000 in the U.K. While the letter stated it was up to each individual to decide whether the U.K. should "remain" or "leave", it encouraged employees to vote. Experts predict that a low voter turnout could swing the polls towards a "leave" vote.  

The letter comes as the latest YouGov poll for The Sunday Times poll shows British support for a "Brexit" is narrowly in the lead. Online betting company Betfair has said more money is now being placed on "Brexit" — according to its forecasts, there is a 34% chance of a "leave" vote. These latest findings rattled the pound, which hit a two-month low in early trading, losing 0.5% to $1.418.

Racke and Patterson, along with Communications Worker Union Deputy Secretary Andy Kerr and Prospect's National Secretary Ben Marshall, said that the vote was so important that they "had an obligation" to write to explain why they supported remaining in the EU was so critical.

The vote will likely have an impact on the economy, and have a "knock-on" impact on companies operating in the U.K. — including BT. That is one of the reasons BT "favors remaining inside a reformed EU," the letter said, adding "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 BT chiefs are not alone in voicing their support for remaining in the EU. Other bosses—including BP (BP - Get Report) boss Bob Dudley, have said it would be a threat to investment if the U.K. leaves the EU. And in February, almost 200 business leaders signed a letter calling on the U.K. to remain in the EU.

The nation, the BT letter continued, has already seen an economic downturn as a result of uncertainty over the looming vote. It has also affected the value of the pound, it noted, which "affects everything from holidays to imported goods."

What's more, EU membership helps British companies to export, the letter said — something key for BT, which earns one-fifth of its revenues outside the U.K. Membership "guarantees we face minimal import taxes or other trade barriers when we provide communications service sand IT support across the EU's 28 member states."

U.K. Chancellor of the Exchequer George Osborne, one of the government's chief proponents of the "remain" campaign, today called for businesses to voice their concerns for "Brexit" ahead of next week's vote.