Ryanair is spamming its customers with Remain emails

Low-budget airline Ryanair is sending an email to over five million of its customers today, urging them to vote for the UK to remain in the EU in the June 23 referendum, according to Sky News.

Ryanair CEO Michael O'Leary has been a vocal advocate of Britain staying in the EU, even hosting a Remain campaign speech by Chancellor George Osborne at Stansted Airport last month.

A source confirmed to Sky News that the email will contain the following:

As the UK's largest airline, we are absolutely clear that the UK economy and its future growth prospects are stronger as a member of the European Union than they are outside of the EU.

A Remain vote will lead to more job creation, stronger economic growth, more foreign direct investment - and more importantly, even more low fares.

We agree the EU needs reform, but we need the UK to remain in the EU to drive this change. We urge all British citizens to vote Remain on 23 June. Just don't miss the registration deadline of 7 June.

Sky News says the email will also feature promotions for Ryanair's European flights.

The email will not sit well with those backing the Leave campaign. Last month a Ryanair "Brexit Special" offer, which gave discounts to British expats flying back to the UK to vote on the day of referendum, was called "bribery" by Vote Leave.

Michael O'Leary is not the only airline boss against a Brexit. Virgin Atlantic founder Richard Branson said in March that a Leave vote would lead to an "unfriendly" Britain and that low-cost airlines like easyJet and Ryanair - who depend on EU membership - would suffer.

Polls suggest the outcome of the referendum is still too close to call. A recent ICM phone poll suggested a four point lead for Leave, but that could be an anomaly as it was conducted over the bank holiday weekend - a period that often records strange results.

Ryanair did not immediately respond to a request for confirmation of the email.