Health insurer Cigna Corp. has announced plans to buy pharmacy benefit manager Express Scripts Holding Co. for $52 billion, the latest tie-up in the health care industry.

But in joining forces, the companies may not have an easy road in front of them. That's because both of the U.S. government's antitrust agencies are likely to continue their trend of aggressively challenging health care mergers, according to a new Crowell & Moring report on regulatory challenges various industries will face this year.

Paul, Weiss, Rifkind, Wharton & Garrison and Wachtell, Lipton, Rosen & Katz represented Cigna, of Bloomfield, Connecticut, while Skadden, Arps, Slate, Meagher & Flom and Holland & Knight represented Express Scripts. None of the firms responded to requests for comment for this report by deadline.

Express Scripts, headquartered in St. Louis, Missouri, was the last big independent pharmacy benefits manager with 80 million prescription plans, so completion of the deal would leave none left for smaller insurers, according to the New York Times. That could mean even more scrutiny by regulators.

The health care portions of the law firm's annual Regulatory Forecast, titled “Digital Transformation: The Sky's the Limit,” explore how companies can help shape regulatory outcomes in an era of cutting-edge technologies.

“The U.S. government has made it a top priority to make sure that any consolidation in the health care industry doesn't hurt competition, and it has been aggressive in trying to block mergers that it believes will hurt consumers,” according to the health care portion of the report, co-authored by Crowell & Moring antitrust partners Joseph Miller and Alexis Gilman.

As examples, Miller and Gilman cite the U.S. Department of Justice's two victories in this area last year: separate federal judicial rulings blocking Aetna Inc.'s $37 billion takeover of fellow health insurer Humana and Anthem's $54 billion proposed merger with Cigna.

In addition, in late 2016, the Federal Trade Commission also won antitrust battles when separate appellate court decisions sided with the agency's efforts to block two mergers of  hospital systems: Chicago's Advocate Health Care Network's proposed combination with NorthShore University HealthSystem, and the tie-up of Penn State Hershey Medical Center and PinnacleHealth System in the Harrisburg, Pennsylvania, area, the report stated.

Although all of these cases were blocked, they provide “helpful intelligence” about the kinds of acquisitions and mergers companies may successfully pursue in the rapidly changing health care landscape, Miller and Gilman said.

“The most important takeaway is that 'horizontal' combinations of head-to-head competitors, as all the blocked cases were, may face significantly greater antitrust hurdles than 'vertical' mergers, in which the merging companies have complementary businesses and don't compete,” they wrote.

Given this heightened level of federal scrutiny of planned mergers, health care companies wanting to “bulk up through acquisitions” may consider turning to their state legislatures for so-called state action immunity, Miller and Gilman said. In such cases, they add, states have legislatively created a state system of active regulatory oversight that displaces federal antitrust laws.

“But the U.S. government isn't likely to sit back and watch if too many more hospital systems that it would have otherwise blocked from merging decide to seek state help,” the authors said.

Added Miller: “If you see a continuing trend toward hospitals seeking immunity to get deals done, you can anticipate a counterreaction from the federal government.”

Other areas of health care regulation that companies may expect to see in the upcoming year include the exploration of blockchain technology as a means of addressing the significant challenges associated with managing large amounts of health data; and continuation of the strong focus on opioid-related cases in the investigation of health care fraud, according to the report.