A migraineur is classified as having chronic migraine when migraines occur on 15 or more days a month. Other factors may be considered.
Chronic migraine is recognized under the Americans with Disabilities Act, and this may assist the working migraineur's ability to function in the workplace. Depending on individual triggers, migraineurs may in some circumstances be able to request accommodations from their employer so that they may perform their duties without bringing on a migraine. This will generally vary based on location, employer, and job description.
Some migraineurs may qualify for social security disability payments, if their migraines match certain conditions and they otherwise qualify. 
- "Accommodation and Compliance Series: Employees with Migraine Headaches." Job Accommodation Network. http://askjan.org/media/Migraine.html#ADA See Also: EEOC Regulations To Implement the Equal Employment Provisions of the Americans With Disabilities Act, as Amended, 29 C.F.R. § 1630. Legal Information Institute. https://www.law.cornell.edu/cfr/text/29/part-1630.
- "Chronic Migraines and Social Security Disability." http://www.disability-benefits-help.org/disabling-conditions/chronic-migraines