Suspending Trading due to Volume

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We have a client with a 401(k) that includes employer stock. The employer has an administrative wherein when volume is extremely high (determined pursuant to pre-defined volume), trading is suspending until such time as the the employer can dispose of all the stock to purchase the new investment. Individuals who immediately prior to the trigger get the average price for the stock when disposed of. The employer does not exercise discretion in suspending trading, it is an automatic trigger once the criteria is met. Does the above create a problem and/or is it impermissible? I have looked for DOL guidance, but thus far have not been able to find any.