Our hotel has "changed" the way an employee receives their banquet tip share - we used to average about $12.50/hr and now it is around $7.50 is this legal?

I know that this seems unfair but it is probably legal.  Most employment relationships are what is known as "at will".  This means that basically the employer can hire or fire someone for any reason or no reason whatsoever, as well has increase/decrease salary/hours, promote/demote, and generally impose requirements as they see fit.  In turn, you can work for an employer, or not, your choice. 

The only exceptions to the above would be if there is a stated company policy covering this, or there is a union/employment agreement that governs, or this situation has arisen due to some type of discrimination.

Note:  An employer can not decrease wages lower the minimum wage which is currently $7.25 per hour.