Disagreement over provisions intended to ensure affordability of vaccines and other medications is holding up agreement on an emergency funding package to fight the novel coronavirus-caused illness that has killed over 3,000 worldwide, sources familiar with the talks said.

Republicans are raising concerns that Democrats’ proposals would chill research and development and interfere with the development of a vaccine, according to sources who spoke without being identified so they could talk freely. Republicans say they share the goal of making sure a vaccine is affordable, but do not want to suppress its development.

But senior Democratic aides said they are not advocating price controls. “Democrats want the supplemental to include significant funding for the federal government to purchase large quantities of coronavirus diagnostics, treatments and vaccine [when it becomes available], which will then be made available to the public without cost,” one aide said.

Another aide pointed to what was done during the 2009 swine flu outbreak. Congress provided $7.65 billion in a supplemental appropriation, part of which was for government vaccine purchases and the cost of planning and implementing a nationwide vaccination campaign.

Democratic negotiators were also pushing to ensure “fair and reasonable price” standards in existing contracting regulations are adhered to for new purchases of vaccines and other medications to treat COVID-19, the illness caused by the new coronavirus. An aide said that would prevent drugmakers from charging above-market rates.