What a judge can — and can't — do in ruling on the Justice Department's deal with CVS and Aetna

A federal judge is considering halting the integration of CVS Health and Aetna — even though the two companies closed their merger last week.

Enacted in 1974, the Tunney Act slows the merger process and adds a layer of oversight in cases where the Justice Department negotiates with the companies seeking to combine. The law created a 60-day comment period and gave judges the final say on whether the agreements made are in the public’s best interest.

Under the law, judges can conclude that the remedy proposed does not address anti-competitive concerns outlined in the complaint, said Jim Tierney, a partner in Orrick’s antitrust practice. They can’t, however, block the entire merger.

That means in the CVS-Aetna case specifically, Leon can decide whether the agreement the Justice Department struck with CVS and Aetna on their Medicare Part D businesses addresses anti-competitive issues, Tierney said. He can find the agreement sufficiently clears these concerns or not. If he finds it does not, the companies can renegotiate with the Justice Department or appeal the ruling.

Leon on Monday said he will order both parties to submit their arguments as to why he should not halt the integration pending his final ruling. He ordered the companies to submit filings by Dec. 14 and called another hearing for Dec. 18.

“CVS Health and Aetna are one company, and our focus is on transforming the consumer health experience,” CVS said in a statement.

Correction: This story has been updated to clarify the judge’s statement as to what order he will issue.