Hi, folx, This is my 1st round in this forum. Glad 2 be here.
Well, regard to the question, according to Babylon dictionary is:
A work card is like an Identity Card which verifies that a person has been given work, or is eligible to perform work in a given profession or jurisdiction. The work card is not a work visa, although it may be used in conjunction with a work visa, permanent resident card or other documentation.
Work cards are often used in countries with high unemployment to certify that the individual meets certain legal requirements (such as head of household, or with dependent children) making him or her eligible for work.
Work cards are also used in certain industries like construction (where specialized training and safety skills are required) or gambling (where background and credit checks are required to reduce the incidence of crime).
Hope it helps.