When he was gunned down by an assassin’s bullet in 1968, Dr. Martin Luther King Jr. was in Memphis. His last political act was to support sanitation workers as they fought for economic security and dignity on the job. Dr. King understood that the struggle for equality and justice is not limited to civil rights. It also includes economic justice. So, as he led the great struggle for civil rights, he also fought for labor rights.

King was in Memphis to support a union because he knew that unions help lift the fortunes of working people in this country. Union jobs built America’s great middle class by lifting families out of poverty, by strengthening communities, and by providing workers with a voice in shaping the direction of our nation. Labor unions also played a powerful role in advancing the fight for racial justice and equality during the civil rights era, mobilizing members and providing financial support.

As the United States continues to grapple with racial and economic inequality, what was true during King’s time remains true today: When workers come together in a union, they gain power to win better wages and benefits for themselves and their families.

But over the last several decades, big corporations, billionaires, and their Republican allies in Washington have waged a war on working men and women through brutal anti-union efforts. These powerful interests have run a coordinated campaign in Congress, in state houses, in executive-branch agencies, and in the courts to rig key decisions in favor of employers at the expense of workers.

If the Supreme Court sides with powerful corporate interests in the Janus case, unions will be forced to represent workers who choose not to pay dues. That’s not fair — and it means that unions could lose a significant portion of the resources they use to negotiate fair contracts. Such a ruling would deal a blow to the freedom of working people in Massachusetts and across the country to band together to fight for fair wages, decent benefits, and a better future.

When powerful corporate interests succeed in weakening unions, they undermine all workers’ economic security. Income inequality gets worse, and the wage gap by gender and race gets worse. The data bear this out: The difference in wages between women and men in unions is far smaller than in nonunion workplaces, about 6 cents for men and women in unions, while nonunion women still earn only 78 cents for every dollar a man makes.

The consequences of the Janus decision could be even more serious for people of color, who constitute a larger portion of the public sector workforce than the private sector workforce. More than half of black workers and almost 60 percent of Latino workers make less than $15 per hour.Union jobs are a path to the middle class for people of color. Black union members today earn about 16 percent more — and Latino union workers about 25 percent more — than their nonunion counterparts. In many industries, the difference is even greater. In addition, most union jobs come with benefits. More than 76 percent of black women in unions have health insurance, while just over 50 percent of nonunion black women do.

The fight to protect and to grow the labor movement is about strengthening America’s middle class and building opportunities for all our families — and we will not back down from that fight.