Large pharmacies like Walgreens have more and more bargaining power when it comes to pricing generic drugs, reports Reuters.

Walgreens formed a drug-buying partnership with AmerisourceBergen in 2013, and earlier this year partnered with pharmacy benefit manager Express Scripts Holdings Co. Retailer CVS Health Corp has tied up with Cardinal Health and, more recently, Wal-Mart has joined with McKesson Corp to source generic drugs. Industry analysts said the alliances took some time to become effective, but their power over negotiations is becoming clear.

“There’s no question those guys are getting much better pricing and really squeezing the manufacturers on margins,” said Gabelli & Co portfolio manager Jeff Jonas. “It’s going to be a tough space for some time … they are just going to keep playing the manufacturers off against each other.”