Anti-union propaganda has a long and distinguished history, going back to the founding of labor unions in the 19th century - it would be hard to capture all its permutations in a single post.

But a watershed moment came during the decades following the Second World War, as some corporate leaders - resentful of the New Deal, riding a wave of anti-communist hysteria, and emboldened by the 1947 Taft-Hartley Act - engaged in a far-reaching public relations campaign to promote free-market values and denigrate labor unions. I'd recommend Kim Phillips-Fein's Invisible Hands: The Making of the Conservative Movement from the New Deal to Reagan for a full discussion of how and why this campaign unfolded.

Phillips-Fein takes issue with the conventional view that neo-conservatism was a backlash against the radical political movements of the 1960s. Instead, she argues, it was also the result of a concerted effort by corporations to shape public culture in a way that benefited their own economic interests.

One of the key figures in this campaign was Lemuel Boulware, General Electric's vice president of labor and community relations in the 1950s and 1960s. Boulware campaigned relentlessly against labor unions, believing they represented a threat to free-market capitalism, using the charismatic Ronald Reagan as a spokesperson to deliver his message through pep talks and radio and television programs. He also devised the practice of "Boulwarism", a tactic that presented unions with take-it-or-leave-it proposals that were meant to undermine the authority of union leadership. According to Phillips-Fein,

Boulwarism represented a new way of thinking about workers, as a kind of captive political audience, a group of people who could be organized to oppose the New Deal and liberalism through lectures, reading groups, and political messages. Boulware never believed that the working class was inherently liberal or Democratic. The union organized workers in one way; his program sought to organize them in another. Instead of being radicalized on the job, they could be instructed in the ways of the marketplace. Corporate culture could be used to reinforce a set of conservative political beliefs, and middle managers could be turned into organizers. Yet this dream revealed the tension inherent in the entire vision of free-market utopianism taught and transmitted through the corporate structure. The idea of the market was supposed to be one of freedom and individuality, yet in the workplace it was taught in rigidly top-down fashion, with the managers and supervisors playing the role of teachers to a subordinate audience. Few other companies during the 1950s made such a radical attempt to shape a corporate culture (although other companies, such as Wal-Mart, would do so later on).

GE led the charge in this campaign against unions, but other corporations funnelled large amounts of money into similar forms of outreach, which inevitably tarnished the reputation of labor unions in the public eye.

See also: Elizabeth A. Fones-Wolf, Selling Free Enterprise: The Business Assault on Labor and Liberalism, 1945-60

Just to make sure since you don't specify, are you from the united states and are you asking specifically about the history there?