If you have an ownership interest in an LLC, you are a member (as opposed to a shareholder). Your rights are determined under the Illinois Limited Liability Company Act. As a member, you have a right to access the corporate books. That is the place to start. If he is not responding to you, you should contact an attorney and have an attorney right a stern letter, informing him of your rights as a member under the law and of the consequences of not providing access.
Based on the few facts you have given, it is uncertain whether you might have an "oppression" claim. An option short of an oppression claim would be an action to require an accounting. One word of caution is in order: depending on the provisions in the operating agreement (if there is one), a suit against fellow members could trigger the dissolution of the LLC. You will want to explore your rights and the ramifications of taking action carefully with an attorney before you draw any lines in the sand.
Answered on Sep 10th, 2013 at 2:09 PM