This op-ed column was originally published at WSJ.com

By Akash Chougule

The new Democratic National Committee chairman’s rocky start has gotten a bit rockier. Following an uncharacteristically contentious and high-profile election, former Labor Secretary Tom Perez narrowly beat Rep. Keith Ellison of Minnesota for the job. Fearing backlash from progressives who supported Mr. Ellison, the Democrats tried to keep the ballots secret. That violated the DNC’s bylaws, and they released the roll call results on Monday after prodding from Wall Street Journal reporters.

This is the height of hypocrisy: The Democratic Party tried to get away with covert voting in its own elections, but when it comes to American workers, it sings a different tune.

For years Democrats—following union marching orders—have sought to deny millions of workers the protection of a secret ballot in union elections. Organized labor prefers that employees make these choices openly, often in front of union organizers or on the doorsteps of their own homes. These “card check” elections allow unions to see exactly who stands with or against them—making countless workers vulnerable to harassment and intimidation.

Mr. Perez has long supported card-check campaigns and opposed secret ballots. Speaking at an AFL-CIO event in 2010 (when he worked in the Justice Department), he called for passage of the Employee Free Choice Act, which would have enabled unions to bypass secret ballots altogether and exclusively use card-check campaigns. That legislation died after failing to secure enough support in the Senate, even though Democrats held a lopsided majority.

As labor secretary, Mr. Perez also embraced regulations meant to limit the information available to workers voting on unionization. Most notable was the administration’s “ambush election” rule that took effect in 2015. The regulation did away with the 25-day wait between when a union election is ordered and when it is held. Labor followed that up last year with its “persuader rule,” which required employers to disclose to the Labor Department any conversation with outside counsel about union efforts. A federal judge in Texas issued a permanent injunction against the rule in November, after earlier having called it “arbitrary, capricious, and an abuse of discretion.”

The reason Mr. Perez and unions support card-check and other coercive tactics is simple: They are effective at bullying fence-sitting employees into union membership. It has been in the union playbook for decades.

The AFL-CIO’s 1961 Guidebook for Union Organizers says: “NLRB pledge cards are at best a signifying of interest at a given moment. Sometimes they are signed to ‘get the union off my back.’ ” In a survey of unionizing campaign outcomes published by the AFL-CIO in 1989, the labor group conceded “it is not until the union obtains signatures from 75% or more of the unit that the union has more than a 50% likelihood of winning” a secret-ballot election.

United Food and Commercial Workers organizer Joe Crump was more direct. He wrote in a 1992 article for the journal Labor Research Review: “If you had massive employee support, you probably would be conducting a traditional” secret-ballot election. But with card check, Mr. Crump noted, “you don’t need a majority or even 30% support among employees.”

The data back up these assertions. A 2009 analysis by the law firm Foley Hoag found that when British Columbia required secret ballots from 1984-92, unions won 73% of elections. After 1992, when the government allowed card-check campaigns, unions won 91%. In 1999 the AFL-CIO’s George Meany Center for Labor Studies analyzed 100 card-check campaigns. The union won nearly 80%, compared with under 50% of secret-ballot elections.

Democrats and Republicans alike should be willing to extend private voting rights to American workers, and the Employee Rights Act is a good way to do it. Introduced in the last Congress by then-Rep. Tom Price (R., Ga.) and Sen. Orrin Hatch (R., Utah) and expected to be reintroduced this year, the bill provides secret-ballot protections in all union elections. It’s a measure that even union households can find easy to support.

Whether voting for the president of the United States or a city councilman, U.S. citizens have long enjoyed the privacy of secret ballots in the voting booth. Members of Congress from both parties should ensure Americans are given that protection in the workplace too.

Akash Chougule is director of policy at Americans for Prosperity.