In the last half-century of American organized labor, the deck has rarely been so stacked against workers, say labor historians.

When it comes to union-busting, employers' tactics are more pervasive than previously thought, according to a new working study produced by the Institute for Social and Economic Research and Policy. The study found that nearly 50 percent of all serious allegations of union busting tactics -- both legal and illegal -- by employers happens after workers express initial interest in a union, but before an official petition has even been filed requesting a vote on union representation.

The length of time -- and the pressure from employers -- between initial interest in a union and the election to determine whether employees wish to organize, the study argued, can significantly influence whether or not workers will get union representation.

"The cumulative effect of the steady, pervasive, and intense employer opposition undermines workers' attempts to exercise their rights to choose union representation free of coercion and intimidation," the study argued, concluding that the period between the petition and the election should be reduced to the shortest number of days possible.

The report comes a week after the National Labor Relation Board proposed new rules that if adopted, could make the road to unionization easier by streamlining the election process and -- most critically -- shortening the length of time between organizers gathering a sufficient number of signatures from workers and a union vote.

Typically, elections take place within two months after a petition is filed. The new rules would shorten that time period, though it's unclear by how much. Labor advocates say that almost any compression of the time period would be a good thing: For employees seeking to join a union, each day that passes is another opportunity for the employer to engage in crushing -- and often successful -- anti-union strategies.

"Employers have gotten emboldened," said Kate Bronfenbrenner, co-author of the study and a labor historian at Cornell University who has written extensively about anti-union strategy. "Employers have always opposed organizing, but what they are doing now shows that they are more and more confident that they are going to get away with it."

Bronfenbrenner laid out the numbers: Twenty years ago, she said, only 29 percent of employers threatened that a workplace might close if a union election succeeded. Along with threatening to fire pro-union employees, threatening to close a workplace is an illegal and increasingly common tactic employers use to intimidate employees in the run-up to a vote. Ten years ago, 50 percent of employers threatened a store closing, and, Bronfenbrenner continued, the most recent data drawn from the NLRB's document database of unfair labor practices, shows 57 percent of employers making such threats.

"The question is whether workers can survive the gauntlet another day, another week," Bronfenbrenner said. "Because every day, every week, that goes by that they have to go through the intimidation and coercion and threats that make up an employer campaign is one more day that makes it more difficult for them to exercise their right to organize."

Examples of attempts to organize derailed by aggressive anti-union tactics are numerous. In 2003, the last year of the study's sample, 3,746 petitions filed, but only 2,438 made it to vote; of those, more than 40 percent were lost by the union. Critics of organized labor attribute this to the unions' waning value in a global economy. But labor historians say that union-busting tactics and the laws that enable them play a far bigger role in the decline of American organized labor.

Earlier this month, a union vote at a Target store outside New York City failed after a majority of employees had already signed cards supporting unionization. Pro-union employees and organizers at the United Food and Commercial Workers union swiftly alleged wrongdoing.

"Target won through fear," one employee told The Huffington Post on the morning after the vote. The UFCW has filed numerous charges with the National Labor Relation Board, accusing the company of "unlawful denial of access to the store, unlawful dress code policy, unlawful no solicitation policy, unlawful use of social media policy as well as threats, interrogation and surveillance" -- even threatening that the company would close the store. Target broadly disputes the union's accusations and denies allegations that it threatened store closure.

One explanation for the upsurge of union-busting tactics, labor experts say, is how weak the disincentives are for employers. Under U.S. labor law, no punitive damages are allowed.

"There's actually a perverse incentive for employers to violate the law," said Dorian Warren, a co-author of the study and a Columbia University professor who specializes in organized labor. "It's cheaper to fire a couple of workers then let a union vote succeed. The employer sends a signal to the entire workplace, and if they lose in a couple of years, all they have to do is pay backpay and post a sign. "