Doctors Without Borders has a message for pharma giant Pfizer pfe : We don’t want your charity.

The global health care philanthropy (known as Médecins Sans Frontières or MSF in much of the world) is turning down Pfizer’s significant offer of one million free pneumonia vaccines to administer to at-risk children.

Rejecting the no-cost medicines didn’t come easy, explained Doctors Without Borders’ U.S. executive director Jason Cone, but was ultimately necessary. “Free is not always better,” said Cone in a blog post, while admitting that telling Pfizer CEO Ian Read that his organization isn’t interested in the free shots was a “difficult task.”

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Cone pointed out that donation offers such as the one that Pfizer made often come with caveats that restrict exactly where the vaccines can be administered and who can receive them. That can actually wind up slowing down vaccination campaigns during public health emergencies. (Pneumonia kills about one million children every year.)

Cone also emphasized that donations can serve as a shield for big pharma companies to excuse drug price hikes. In fact, Cone argues that the tactic can actually be anti-competitive, discouraging other entrants into the vaccine market which might have otherwise helped reduce prices for all customers.

“We need competition from new companies to bring down prices overall — something we don’t have currently for the pneumonia vaccine,” he wrote, adding that donations “are often used as a way to make others ‘pay up.’

“By giving the pneumonia vaccine away for free, pharmaceutical corporations can use this as justification for why prices remain high for others, including other humanitarian organizations and developing countries that also can’t afford the vaccine. Countries, which continue to voice their frustration at being unable to afford new and costly vaccines such as [the pneumonia vaccine], need lower prices as well to protect children’s health,” Cone wrote.

Cone did praise another pharma giant, GlaxoSmithKline gsk , for recently reducing its pneumonia vaccine price to the lowest in the world for humanitarian organizations and urged Pfizer to take a similar path. Glaxo has been pursuing a striking pricing model to make therapies more affordable in developing nations under the leadership of outgoing CEO Andrew Witty. (The company won the top stop in Fortune’s Change the World list for this and other efforts this year.)

“Pfizer strongly disagrees with MSF’s stated policy and believes product donations play a crucial role in addressing humanitarian crises around the world,” a company spokesperson emailed Fortune in a statement. “We reiterate our offer of 1 million free doses and continued supply to meet these urgent, emergency needs.”

Update: October 13, 2016, 2:45 pm; This post has been updated to include a statement from Pfizer.