The answer is the Equal Rights Amendment (ERA)
The proposed Equal Rights Amendment was meant to guarantee equal legal rights for all American citizens regardless of sex. However, it was never ratified.
The amendment won the requisite two-thirds vote from the U.S. House of Representatives on October 12, 1971. And months later, on March 22, 1972, it was approved by the U.S. Senate. Therefore it was sent to the states for ratification with a deadline of March 22, 1979.
Although the ERA soon gained ratification of 30 states, a highly organized group of conservatives (religious and political) came in the way, opposing the ERA and stopping the ratification. These groups argued that the amendment approval wouldn't be of such benefit for women nor the society as for women would lose privileges and protections such as exemption from compulsory military service, combat duty, economic support from husbands for themselves and their children, among others.
The ERA's deadline was then extended to June 1982, but still, it didn't get to be ratified by the requisite majority of 38 states.