CVS, which stopped selling tobacco products in September, is taking steps to pressure other pharmacies to do the same, according to The Washington Post.

Some customers will soon be required to make a $15 co-payment on prescriptions filled at non-CVS pharmacies that sell tobacco products, under new rules issued by Caremark, the pharmacy benefits management arm of CVS.

The rules will encourage customers to fill prescriptions at CVS-owned pharmacies. They will also put financial pressure on other pharmacies that are part of the Caremark network to stop selling tobacco products, the article notes. More than 54,000 pharmacies are part of the Caremark network, including more than 20,000 independent pharmacies.

“For clients who choose a tobacco-free network, plan members would be provided with a full list of participating pharmacies in advance of any network change,” CVS spokeswoman Carolyn Castel told the newspaper. “A tobacco-free network would include CVS/pharmacy and Target nationally as well as other local or regional pharmacies including numerous independent pharmacies that do not sell tobacco products.”

A new study, funded by an unrestricted grant from CVS, found 6 percent of people who went to the pharmacy to pick up asthma or COPD medicine also made at least one cigarette purchase within the same week. The researchers found 5.1 percent of people taking high blood pressure medicines and 4.8 percent of those buying oral contraceptives also purchased tobacco products.