Can an employer reduce pay if there is a current contract for a certain amount of pay?

Yes, unless the reduction in pay results in less than minimum wage or the failure to pay overtime to non-exempt employees.  However, if a certain pay is gauranteed by an enforceable contract, which is truly rare, and the employer is failing to pay the gauranteed rate, then there may be a contract claim.  You would need to read the contract to see if it says what will happen if the employer does not pay the gauranteed rate.