The park is being hired out exclusively to the Muslim Research and Development Foundation (MRDF) and its allied organisations.
The MRDF, based in the east London borough of Tower Hamlets, is run by Haitham al-Haddad, who has been banned from speaking at a number of British universities due to his anti-Western views.
He believes music should be banned, that men and women should be segregated, and is a leader of a campaign to build a massive mega-mosque close to the Olympic Park in east London.
Some point out that many Christian and Jewish leaders also hold “extreme” views on homosexuality, but others say he is an “outright homophobe” who should not be influencing young children.
His MRDF charity earned £260,000 in 2012 and it has a growing influence.
It attracted controversy last November when it hired out the Chessington World of Adventures theme park in Surrey for an Eid Fun Day.
The charity said because that event was so successful, it decided to hold another one at Legoland whose season officially starts five days later on March 14.
As such the park is being hired out privately and it is likely only Muslim families will attend.
Tickets are being sold for £17 and coaches will depart from the East London Mosque in Whitechapel that morning.
The organisers’ website reads: “By the Grace of Allah, on the back of our highly successful 1st Eid Fun Day at Chessington World of Adventures – we are launching our 2nd Family Fun Day at Legoland Windsor Resort – with the hope that the two events will become the standard and annual fundays for decades to come, insha’Allah.
“Family Fun Day is a family centred event where we aim to bring Halal entertainment/environments for Muslim families in the West.
“The aim is to provide a true alternative in which like minded families can enjoy safe and enjoyable time while at the same time conducive to their faith.”
However, there are fears they will encounter protesters from the far right when they arrive.
Tom Bursnall, a Ukip councillor in Windsor, said there was “a great deal of resentment building up against Legoland” in the town.
He said: “There should be a peaceful demonstration. Residents are up in arms about this.
“They’re astonished Legoland is hiring itself out to man who promotes such sinister views.”
“We certainly do not discriminate in any way.”
A message on Legoland’s Facebook page reads: “The removal of the page was requested by the Thames Valley Police as an investigation is currently underway to identify those responsible for some of our wall posts, private messages, phone calls and emails.
“Anyone posting or thinking of posting offensive and threatening messages on this page or other social media sites should be aware that the Thames Valley Police are monitoring the situation closely and we will not hesitate to take robust and swift action against anyone engaging in this type of activity.”