Question

According to the chart, union membership peaked around.

Answer 1

 The number of union members peaked in 1979 at an estimated 21.0 million.
This was the priod before government create regulations that set a certain standard for payment that imposed for the companies.
Before such standard was created, many companies openly gave wages below the standard of living, and many workers united in order to obtain fairness in their contract agreement

Answer 2

According to the chart, union membership peaked around 1945 .

Membership began steadily to decline after 1970.

In 2000, about 12 % of workers were members of a union.