Many law firms earlier this year went out of their way to encourage COVID-19 vaccines without mandating them. But now more Am Law 200 law firm leaders are getting strict, implementing new restrictions and forcing personnel to get shots in their arms—or else get shut out of the firm’s offices.

What’s changed? Besides the surge of cases due to the contagious delta variant and new guidelines from the Centers for Disease Control and Prevention, other factors are at play. A push by large corporate clients, as well as the need to keep some semblance of office return plans, have also contributed to a wave of law firm vaccine mandates, firm leaders and legal industry observers say.