Nine biopharmaceutical companies have signed an unusual pledge to uphold "high ethical standards," suggesting they won’t seek premature government approval for Covid-19 vaccines.

The pledge, released on Tuesday, states: “We, the undersigned biopharmaceutical companies, want to make clear our on-going commitment to developing and testing potential vaccines for COVID-19 in accordance with high ethical standards and sound scientific principles.”

The companies that signed up to it are: AstraZeneca, BioNTech, Moderna, Pfizer, Novavax, Sanofi, GlaxoSmithKline, Johnson & Johnson and Merck.

The pledge comes just about a week after US Food and Drug Administration Commissioner Dr. Stephen Hahn said the agency could consider emergency use authorization or approval for a Covid-19 vaccine before critical Phase 3 trials are complete.

The nine companies on Tuesday wrote that they pledge to “Only submit for approval or emergency use authorization after demonstrating safety and efficacy through a Phase 3 clinical study that is designed and conducted to meet requirements of expert regulatory authorities such as FDA.”

Pfizer and Moderna have vaccines in late-stage, Phase 3 clinical trials in the United States; Johnson & Johnson is preparing to start one.