My employer has decided to get uniforms for it's employees. The employees will also be paying for half the cost of the uniforms. Is there a law in Louisiana that states the employer must pay the full amount for uniforms? Can the cost of the uniforms be deducted out of our paychecks without us signing anything?

Louisiana doesn't have much in the way of wage payment laws, and I couldn't find a law requiring written authorization, although the employer would be dumb not to.

The deductions cannot bring the employees below minimum wage under federal law.

Agreed. Also the federal rules do not require written authorization for uniform deductions (or much of anything else), so the state would have to have it's own rules specifically requiring written authorization. And Louisiana is one of several states that does not have much in the way of labor laws.

http://www.dol.gov/esa/regs/compliance/whd/whdfs16.htm