The email was dated January 30 but made public in the past 24 hours.
Hilaire said the WICB rules conformed to the ICC's operating manual and that a player would be granted an NOC to play a domestic tournament in another country on the condition that he be available for selection if an international series clashed with the tournament.
"So, Chris, it is your choice, whether you receive a conditional or unconditional NOC. But you cannot have an unconditional NOC and be considered for selection to play for the West Indies," Hilaire wrote in the email dated January 30.
"Either you wish to make yourself available to play for the West Indies, in which case you must accept that NOCs will be granted to you on the same conditional terms as other international players, or you do not, in which case you can have your unconditional NOC. All that is required from you is a clear statement, one way or the other."
"If a player has no contractual obligation to WICB, and does not wish to make himself available to play in international matches for which he may be selected, then he has the option of ceasing to be a FTS (first team squad) Player, by retiring from international cricket, or otherwise declaring himself ineligible and/or unavailable for selection for the foreseeable future. In that event, WICB would not consider it necessary or appropriate to issue a player with anything but anunconditional NOC."
Gayle has not played for West Indies since the 2011 World Cup because of comments he made against the board and the coach Ottis Gibson during a radio interview. The WICB asked Gayle to retract his comments and the batsman has refused to do so. Gayle has just arrived in South Africa to be part of Dolphins' domestic Twenty20 campaign after playing for Barisal Burners in the Bangladesh Premier League.
In his email, Hilaire told Gayle he was "ineligible for selection pending resolution of certain matters."
"The Board requires you to provide a general public retraction of the comments made in the interview in question and the effect it has had on the team, Coach, Captain and Management and to express a commitment to team and management. If the terms of that retraction can be agreed, WICB will be happy to consider you eligible once again for selection."
