semi-final between Spain and the United States between September 19-21.
The president of the Spanish Tennis Federation, Pedro Munoz, prefers the famous Las Ventas bullfighting arena in the Spanish capital but the players are worried that Madrid's 600-metre altitude will favour the US player's faster game.
The Spanish players prefer any of the three other candidates to host the event -- Benidorm, Tenerife and Gijon -- which are at sea level.
Spain captain Emilio Sanchez Vicario and eight other players vowed in an open letter published Wednesday not to take part in any federation event in protest as long as Munoz is its president, describing him as "dictatorial".
"Our only objective is and will always be to represent Spain under the best possible conditions," the letter published on the web site of daily newspaper El Mundo said.
"It is us players who play and defend the colours of our country and we feel we are the main ones to be hurt by the decisions that have been taken," it added.
Among the players who signed the letter was Rafael Nadal, David Ferrer and Nicolas Almagro. It was signed in Rome where the players are taking part in the Rome Masters Series.
The federation will on Friday announce its decision regarding the site for the best-of-five series.
Spanish media have reported that the federation is under pressure to selection Madrid as the site of the Davis Cup semi-final because the city's tourist office is a key sponsor of the event through 2010.
No one from the Spanish Tennis Federation was immediately available to comment on the open letter.
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