A 2000 law, the "Visa Waiver Permanent Program Act" provides that new or amended H-1B petitions usually are not required when the employer company reorganizes or merges with another company.  Click here for the text of this law, or here for a State Department memo that further explains the law. 

However, amended petitions for L-1 employees usually are required.  Also, the company restructuring may impact applications that seek employees' permanent residence status.  A thorough analysis by immigration counsel will ensure that visa employees will remain in valid status and that the company is in full compliance with immigration laws and regulations.