Our club a 501 (c) 7 recently asked for voting approval for a loan of $2million. Their documentation said 2/3 vote of members was required to approve. However, after the vote they said they only needed 51% of the vote to approve. The voting tally would have not allowed them to go forward with the stated 2/3 requirement but did when they changed the requirement to 51%.

There was no notification to members that the 2/3 majroity was changed prior to the meeting.

Is there a way this can be challenged.

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Is there a way this can be challenged.

Possibly. You should examine the corporation code for whichever state it is under which the corporation is organized.