The regulation (law) that addresses your specific question has not changed. However, both employers may be right. Here's why:
The regulations allow the employer to determine, to a certain extent, what is defined as "eligible compensation/pay" for the purposes of determining contributions to the plan. For instance, some plans include overtime pay in the definition of compensation for salary deferral purposes, while others may not.
Here's an example: assume that the plan does not include overtime in the definition of compensation and limits your salary deferral to 10% of your compensation. If you earn $10,000 as regular (straight time) pay and $1,000 in overtime, you would be allowed to defer up to $1,000 to your 401(k) because your limit will be 10% of your straight time pay.
If you cannot contribute as much as you would like to, all is not lost. If you have extra funds you want to contribute to a retirement account, you may consider making a contribution to an IRA.
This question was answered by Denise Appleby