Facebook is facing a possible legal challenge over what has become one of its most popular games, and users are already lining up for battle.

Scrabulous is in the top ten of the social networking sites most popular applications, with almost 600,000 people using it on average every day according to the site's statistics.

However, in a battle of old against new, the joint makers of the original Scrabble boardgame have insisted that the online version be taken down.

Toy manufacturers Hasbro and Mattel have written to bosses at Facebook's US headquarters asking them remove Scrabulous because of copyright issues.

According to The Telegraph, Hasbro owns the rights to Scrabble in the US and Canada and Mattel to the rights elsewhere in the world.

Mattel UK said in a statement: "Letters have been sent to Facebook in the US regarding the Scrabulous application".

"Mattel values its intellectual property and actively protects its brands and trademarks."

"As Mattel owns the rights to the Scrabble trademark outside the US and Canada we are currently reviewing our position regarding other countries."

But Mattel and Hasbro are going to have a battle on their hands.

In little more than a day more than 13,000 people have signed up to a Save Scrabulous group on Facebook.

The page includes a petition to sign as well as contact details for executives, customer service and complaint departments.

The BBC is reporting that many members of the group posted information about the responses they were getting.

Discussion on the group has been critical of the toy makers and some of those visiting have called on Hasbro and Mattel to "back off" and leave Scrabulous running.

Some Scrabulous fans have even said that they would boycott Hasbro and Mattel products if the game disappeared.

Others say that the decision to launch legal action is "short-sighted" as it could not only damage the two makers' reputation but also some fans said that playing Scrabulous had led them to buy a copy of the Scrabble board game.

Scrabulous is a miniature form of the boardgame, which was originally invented in 1938 by an American architect called Alfred Mosher Butts.

However, the game didn't take off until a decade later when a wily lawyer bought the rights to the game, which now sells more than half a million boards each year in the UK alone.

The Facebook version was created in 2005 by Indian brothers, Rajat and Jayant Agarwalla.

Facebook is not commenting on the case.