"Ban the box" is a movement to outlaw employers asking applicants if they have a criminal history, motivated largely by the disparate impact it has on non-Asian minorities due to their higher rates of incarceration. According to the Guardian link above, it's necessary because of "research suggesting that three-quarters of employers admit to using a criminal conviction to discriminate against an applicant." Somehow different from discrimination on the basis of poor references, lack of relevant skills and giving a lousy interview, which only screens out the merely incompetent, not the physically dangerous.
But Britain's Labour Party is now pushing for a "blacklist" to "warn" those same employers about those convicted of "hate crimes" and "tackle the UK’s soaring rise in antisemitism, Islamophobia, homophobia and abuse of people with disabilities." It appears to be part of a larger campaign to purge social media, such as Twitter, of the wrong kind of speech. So employers aren't allowed to protect themselves from, say, a convicted sex offender working in a shop, but must be vigilant against such as Britain's "Tube Racist" lady (convicted to 21 weeks in jail for a "racist rant").