In the short term, the Biden administration said it was using the law to ensure Pfizer has access to needed equipment to scale up production of the vaccine it developed with German company BioNTech. Between that product and the one developed by Moderna, the federal government has contracts in place for 400 million vaccine doses in the first half of the year — enough for 200 million people under the two-dose protocols.

The Biden administration is seeking 100 million more doses from each company, with the aim of securing the additional doses through the summer. While the administration has expressed confidence it will receive the supply, people knowledgeable about the negotiations said the need for certain equipment is vital.

Because Pfizer did not work with the government as closely as other vaccine manufacturers did, including Moderna, it initially did not receive favored treatment under the Defense Production Act, which allows the government to direct suppliers to fulfill certain contracts ahead of others. Giving Pfizer priority for a number of crucial products — such as lipids, the oily molecules needed to produce the vaccine — was among the terms of a deal for additional doses reached by the Trump administration in December, according to people familiar with the discussions.