You can lay off anyone you wish. Check with your labor attorney or the regional immigration office for procedural requirements. Ordinarily there would be none other than paying the return one-way ticket if you are terminating. And, if you bring them back you absolutely cannot deviate from the original job description that was on the petition. Wouldn't it be something if government procedures actually granted employment preference in retention to non citizens at the expense of citizens. They haven't thought of that yet.
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