The Voting Rights Act, signed into law on Aug. 6, 1965, by our father, President Lyndon B. Johnson, opened the political process to millions of Americans.

The law was born amid the struggle for voting rights in Selma and Montgomery, Ala., which the Rev. Dr. Martin Luther King Jr. called "a shining moment in the conscience of man." By eliminating barriers, including poll taxes and literacy tests, that had long prevented members of minority groups from voting, the act became a keystone of civil rights in the United States.

Now, crucial provisions of this legislation are in jeopardy.

Last month, Congress seemed set to renew expiring sections intended to prevent voter discrimination based on race or language proficiency. Instead, a group of House lawmakers opposed to those sections succeeded in derailing their consideration.

The Voting Rights Act prohibits discrimination in voting everywhere in the country. But it has a special provision, Section 5, intended for regions with persistent histories of discrimination. These states and localities must have their election plans approved by the Justice Department.

Since the act was last renewed, in 1982, the federal government has objected to hundreds of proposed changes in state and local voting laws on the basis of their discriminatory impact. In recent years, proposed election changes in Georgia, Texas and other states were blocked because they violated the act.

Yet states and localities are not subject to Section 5 forever. In order to gain exemption, they need only meet a set of clear standards proving that they have been in compliance with the law for 10 years and have not tried to discriminate against minority voters. In Virginia, for example, eight counties and three cities have been exempted from Section 5.

Another section of the act, Section 203, which Congress added in 1975, requires language assistance in certain jurisdictions to promote voting by citizens with limited proficiency in English. There are now 466 such jurisdictions in 31 states.

No one disputes that our nation has come a long way since the Voting Rights Act was first signed into law. But while it would be nice to think we don't need this legislation anymore, we do. We still struggle with the legacy of institutionalized racism. If either of the act's two sections under attack is weakened or allowed to expire, the door will be opened to a new round of discriminatory practices.

The reauthorization stalled in Congress is called the Fannie Lou Hamer, Rosa Parks and Coretta Scott King Voting Rights Act Reauthorization and Amendments Act of 2006. Were he alive today, we believe President Johnson would be honored to have this bill named after such remarkable women. Its passage would be a fitting tribute to their collective efforts to expand the scope of civil rights and citizenship.

In his own era, our father faced powerful opposition to the Voting Rights Act, including from members of his own party. Nonetheless, he pushed forward with the legislation because he knew it was desperately needed. It was the right thing to do then. It still is.

Luci Baines Johnson and Lynda Johnson Robb are the daughters of President Lyndon B. Johnson. They wrote this commentary for The New York Times.