By agreeing to settle several class action shareholder lawsuits over its proposed merger, Cigna Corp., along with fellow health insurer Anthem Inc., can focus on clearing the regulatory hurdles necessary to merge.

Cigna's agreement last week to settle six shareholder class actions filed in Delaware and Connecticut over its proposed merger with Anthem — without admitting liability or wrongdoing — came as Anthem and Cigna shareholders prepare to vote Thursday on the $54 billion deal.

Even if shareholders approve the deal, Anthem and Cigna's proposed combination still faces approval by state and federal antitrust regulators.

When Indianapolis-based Anthem agreed to acquire Bloomfield, Connecticut-based Cigna in July, some Cigna shareholders went to court claiming Cigna breached its fiduciary duties by agreeing to a deal that undervalued Cigna and favored Anthem over competing bids, and that the sales process was flawed due to conflicts of interest, Cigna said in an October filing with the U.S. Securities and Exchange Commission.

Subsequently, in a Nov. 24 SEC filing, Cigna said it had entered into a “memorandum of understanding” to settle the suits “solely to avoid the costs, risks and uncertainties inherent in litigation, and without admitting any liability or wrongdoing.”

In exchange, future claims challenging the merger will be released, the filing states.

Health insurer Humana Inc. in October also agreed to settle similar shareholder class actions that sprang up following its proposed merger with Aetna Inc., which shareholders approved later in the month.

Neither has disclosed the amount of money involved in the settlements.

Shareholder suits are common in large mergers and acquisitions, whether in the health care sector or other industries, experts say.

Shareholder suits were filed when WellPoint Inc. — now Anthem — acquired Amerigroup Corp. in 2012 and when Aetna acquired Coventry Health Care Inc. in 2013, said Tom Mason, senior insurance industry analyst at SNL Financial Inc. in Charlottesville, Virginia.

“If you're a shareholder, you want a better price,” Mr. Mason said. “This is a way to provide some leverage and let the companies know, 'We're your shareholders; we want to be heard.'”

Such lawsuits are simply a “nuisance” for the insurers, and come down to shareholders wanting more money from the deal, said Rob Fuller, of counsel at Los Angeles-based law firm Nelson Hardiman L.L.P.

It's less painful for Cigna to pay a settlement than to participate in a more expensive and distracting legal battle, Mr. Fuller said. That's despite the fact that such shareholder suits in Delaware, where the pathway for merger approval is clearly established, would rarely win, he said, adding that at times, the suits are “fully justifiable,” however.

Despite silencing the shareholder suits, opposition from other corners is unlikely to be quieted, sources said. Physician, hospital and consumer groups have argued the health insurer mergers would reduce competition, leading to higher patient premiums and lower provider reimbursements, and reduce the quality of care.

Still, the big obstacle in both proposed mergers is securing state and federal antitrust approval. Whether the deals will be approved depends on the combined organizations' market share, and that depends largely on how the data is viewed, sources said.

For example, from a national standpoint, the deals probably would not violate antitrust laws, but some divestitures might be needed to land approval on a state-by-state basis, Mr. Mason said.

“It's a close question,” Mr. Fuller added.