When Amazon busted a union drive at its Bessemer, Alabama, warehouse earlier this year, it ran a sophisticated campaign that involved sending text messages and mailers to employees warning them of the downfalls of a union, offering bonuses to employees who quit before the union election, and even allegedly accessing the drop box that employees used to mail their ballots.

But the size and scope of Amazon’s efforts — and who was coordinating them — wasn’t fully visible to the public or to employees partaking in the election, because the Trump administration scrapped a rule that would have required disclosure of certain union-busting expenditures by corporations. The so-called persuader rule was designed to spotlight an industry that rakes in nearly $340 million a year advising corporations on how to prevent their employees from unionizing.

Biden promised during his campaign to revive the persuader rule, but he so far has refused to follow through on the pledge, which could expose the activities of large corporate law firms who offer “union avoidance” services and whose employees funneled big money to Biden’s campaign and the Democratic Party as a whole.