The head of the Food and Drug Administration is questioning whether electronic cigarette maker Juul and its new partner Altria are following through on pledges to help stop underage vaping.

FDA commissioner Scott Gottlieb on Friday posted letters he sent to Juul and Altria, the maker of Marlboro cigarettes and other . He called for a joint meeting to discuss whether they are honoring their commitments to the agency.

In response, the two companies said they are moving ahead with plans to stop teens from getting their products.

Late last year, Altria paid nearly $13 billion to purchase a 35 percent stake in Juul, which now controls most of the U.S. e-cigarette market.

Previously, Altria said it was pulling several flavored vaping brands to be "part of the solution."