Ministry of Sound has started round three in its public campaign against AIM, in protest at Impala's agreement with Warner Music Group.

The dance music company has issued its third, barbed open letter to the U.K. independent music companies' trade association, in less than a week.

In the new document, issued this morning under the headline "AIM in Crisis," MoS demands the immediate resignation of the Impala executives responsible for the pact with WMG.

Impala, the pan-European independent labels trade body, recently forged a contentious - and confidential - agreement with WMG, through which the Brussels-based body vowed to not oppose the music major's approach for EMI Group. MoS, and later Gut, resigned their respective memberships of AIM. London-based AIM is a member of Impala.

MoS' latest letter arrived ahead of AIM's anticipated formal announcement on last night's executive board meeting, at which attendees failed to ratify the Impala-WMG deal. An "emergency" AIM board meeting last week also failed to reach a conclusion.

"As far as we have learned," says MoS in its letter, "the AIM board was unable to ratify the Impala/WMG agreement at its meeting yesterday due to the totally unreasonably restrictive gagging order placed upon it by Impala."

Impala has placed the AIM board and the independent community "in a completely untenable position," MoS says in today's statement. It adds, "Impala has reached an agreement, which AIM has had no involvement in negotiating and Impala refuses to allow the AIM members to see the terms that Impala has agreed."

MoS Music Group managing director Lohan Presencer had attended the early part of the Feb. 28 "emergency" meeting, but took no further part in proceedings when he refused to sign a non-disclosure agreement.

In today's note, MoS admits that it had received a private, six-page response from AIM, but declares that "urgent questions surrounding conflicts of interest as raised by MoS remain unanswered."

Billboard.biz received AIM's formal announcement at 1pm GMT.