This question has been asked so many time that you could have just searched on this topic in this forum. There is no definitive answer to this. A Green Card is issued under the assumption that company has a long term position available for which they could not find anyone in US regional area.
TECHNICALLY, INS can raise the issue that when your company is laying off people, is there really a long term position available for which they need a foreigner.
BUT, I haven't seen a single case where INS applied this strict definition. INS spends most of its energy fighting cases where they detect either some serious fraud , Visa violations or Terrorism related actvivities.
So worry about your job rather than worrying about INS because you can always use AC21 .