What are the similarities between the U.S. Employment Card and the Green Card?

Similar points:

Both can work and prove their identity,

Differences:

With a work card, you can work legally, but You may not necessarily have a green card. If you have a green card, you can work legally and there is no need for a work card.

In the United States, the Social Security number (SSN), commonly known as the employment card, is a set of nine-digit numbers issued to citizens, permanent residents, and temporary (working) residents. It is based on the U.S. Social Security Records of social security cards in Section 205 C2 of the Social Security Act. This set of numbers is issued to individuals by the federal government's Social Security Administration. The primary purpose of Social Security numbers is to track personal tax information, but in recent years it has become a de facto national identification number. A Social Security number can be obtained using the SS-5 application form and is pursuant to Title 20, Code of Federal Regulations, Section 422, Subparagraph 103b.

The United States Permanent Resident Card, also known as the green card, is an identity document used to prove that foreigners have permanent resident status in the United States. "Obtaining a green card" is used to refer to the immigration process of becoming a permanent resident. Lawful permanent residence for green card holders is an official grant of immigration benefits, including conditional permission to remain and work in the United States. The holder must maintain his or her permanent resident status and may lose it if one of the conditions required for the status is no longer met.