Today President Obama is ignoring the lessons of the civil rights era he claims to revere. According to a draft executive order leaked last week, Mr. Obama plans to require any company seeking a federal contract to disclose its executives’ political contributions over $5,000—not just to candidates, but to any group that might make “independent expenditure” or “electioneering communication” advertisements.

If a small businesswoman wants to sell paper clips to the Defense Department, Mr. Obama would force her to reveal contributions to groups such as Planned Parenthood or the National Rifle Association. These donations are obviously irrelevant to whether she made the most reliable bid at the lowest price…

Our era of instant mass communication exponentially multiplies this threat. Supporters of California’s Proposition 8, which bars gay marriage, have faced relentless harassment after a federal court refused to bar the disclosure of their identities in 2009. Opponents promptly created a website that used the Prop 8 list to create a map of donors’ homes. Widespread intimidation followed: Some Prop 8 supporters were fired from their jobs, and several of their businesses were boycotted.

Mr. Obama’s executive order threatens to replicate the Prop 8 experience on a nationwide scale. In fact, it requires the release of contractors’ political contributions in a publicly available electronic database to be posted online as soon as possible.