The ongoing dispute between Express Scripts Inc. (ESRX) and Walgreen Co. (WAG) has reached the courthouse, with the pharmacy-benefit manager accusing the drugstore giant of violating an agreement between the two firms while making disparaging remarks.

The companies have a contract that runs through this year, but renewal talks have broken down amid a public dispute involving different views about which firm is making unreasonable demands. In a court filing made last week, and referenced by an Express Scripts executive Wednesday during a Morgan Stanley conference, Express Scripts seeks to prevent what it sees as inappropriate actions and statements from Walgreen.

"Walgreens has crossed a line and is not negotiating in good faith," Express Scripts said in an emailed statement. "We will not let this stand."

A Walgreen spokesman did not have an immediate comment regarding Express Scripts's allegations.

Companies like Express Scripts handle prescription-drug benefits and claims for employers and health-insurer clients. The company filed its complaint in the U.S. District Court for the Northern District of Illinois.

The complaint alleges "Walgreens has launched an aggressive campaign to disparage Express Scripts, disenroll Express Scripts' commercial and Medicare Part D members and to promote and prefer other Medicare Part D programs to the exclusion of those offered through Express Scripts."

Through the current agreement between the firms, the drugstore agreed it wouldn't attempt to disenroll any Express Scripts member or market one Part D plan over another, Express Scripts said. Their agreement gives Walgreen access to more than 60 million Express Scripts members, including about 2.5 million with Part D prescription drug coverage through the government's Medicare program.

In a court filing, Walgreen said its communications with Part D customers did not violate its agreement with Express Scripts.

The relationship between pharmacy-benefit managers and retail pharmacies has grown more contentious, in part because the benefit managers operate mail-order pharmacies that compete for business. Retail pharmacies have strongly opposed Express Scripts' plan to acquire rival Medco Health Solutions Inc. (MHS) to create a clear industry heavyweight.

Despite the heated nature of the public dispute, Express Scripts has repeatedly said it remains willing to restart talks with Walgreen. Chief Financial Officer Jeff Hall repeated this Wednesday.

"We continue to be available to get to a resolution here," he said at the Morgan Stanley conference.

-By Jon Kamp, Dow Jones Newswires; 617-654-6728; jon.kamp@dowjones.com

--Maxwell Murphy contributed to this article.