Editor’s Note: Steven Greenhouse was a New York Times reporter for 31 years and is author of Beaten Down, Worked Up: The Past, Present, and Future of American Labor, to be published by Knopf this August. The opinions expressed in this commentary are solely his own. Read more opinion articles at CNN.

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Delta Air Lines has taken a beating on social media in recent days for trying to persuade thousands of its employees not to unionize. It put up posters telling flight attendants and ramp workers that the $700 they would pay in annual union dues would be better spent on video games, rounds of beer or baseball tickets.

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While union leaders say these posters insult workers’ intelligence, there is no denying that Delta has had considerable success beating back unionization. (In a statement, Delta said, “Delta has shared many communications, which on the whole make clear that deciding whether or not to unionize should not be taken lightly.”)

Delta is the least unionized major US carrier, and thanks to its aggressive anti-union campaigns, organizing drives by the flight attendants’ union were defeated in 2002, 2008 and 2010. Delta’s flight attendants narrowly rejected unionizing in 2010, with 9,216 voting for and 9,544 against.

Corporate executives, of course, applaud such defeats for labor, asserting that unions impede management’s flexibility and hurt profits. But while any given union defeat may be good for a corporation’s shareholders and managers, the many union defeats, taken together, have taken a substantial toll on workers and society.

The percentage of private-sector workers who are in unions has dropped from 35% in the 1950s to just 6.4% today — from more than one in three to just one in 16. Numerous factors have fueled this decline, including factory closings, outsourcing and automation, but corporate America’s decades-long effort to hobble unions is arguably the biggest factor.

The decline of unions has fueled income inequality and wage stagnation, reduced economic mobility and helped enable corporations and wealthy donors to dominate our nation’s politics and policymaking. When unions were mighty and union jobs plentiful, unions pulled up wages for everyone, nonunion workers too.

Unions catapulted countless number of workers with just a high school degree into the middle class. In their book “Winner-Take-All Politics,” Jacob Hacker and Paul Pierson bemoan the decline of unions, writing, “While there are many ‘progressive’ groups in the American universe of organized interests, labor is the only major one focused on the broad economic concerns of those with modest incomes.”

Unions have also played an important role in reducing inequality. The decades when organized labor was strongest — the 1940s through 1970s — were the decades when America had the least income inequality. It’s no coincidence that the United States has one of the weakest labor movements among major industrialized nations and ranks near the top for income inequality.

One study found that the decline in union power and density since 1973 explains a third of the increase in wage inequality among American men, and a fifth of the increased inequality among women. Economists at the International Monetary Fund found that the decline in unionization explains about half of the rise in incomes for the richest 10% percent in advanced industrial nations since the 1980s and about half the increase in those nations’ main measure of income inequality.

Unions help to reduce inequality by pushing for higher pay for typical workers, greater restraints on executive pay and increased taxes on the rich. Another study found that a 10% increase in the percentage of unionized workers in a US community is associated with a 3% to 4.5% increase in the income of all the area’s children — partly because unions push for better schools and a higher minimum wage.

As union ranks have declined, so has labor’s power in politics. In the 2015-16 election cycle, business outspent labor 16 to one — $3.4 billion to $213 million — according to the nonpartisan Center for Responsive Politics. That center also found that all the nation’s labor unions taken together spend about $45 million a year for lobbying in Washington, while corporate America spends $3 billion — 66 times as much.

Corporate America’s huge advantage in campaign contributions and lobbying explains why many worker-friendly measures that have overwhelming public support stand little chance of being enacted. Americans support raising the $7.25 federal minimum wage; 75% want to see it at $12.50 by 2020. They also want laws guaranteeing paid sick days by 85% to 14%, and employer-paid parental and family leave by 80% to 17%. Corporate lobbyists have long given these a thumbs down, and these proposals have been stalled in Congress for years.

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    Many business executives voice alarm that more young Americans have a positive view of socialism than capitalism, according to a recent Gallup poll. Many young people feel this way because income inequality in the US is so extreme, economic mobility has slowed, and the American dream has become more elusive.

    Strengthening unions would be an important way to help reverse these unfortunate trends. Corporate executives and Wall Street will no doubt cheer if Delta’s ramp workers and flight attendants again vote down unionization, but many economists warn that any further weakening of labor unions will skew our nation toward even greater income inequality and even greater domination of our politics and policy-making by corporations and wealthy campaign donors.