WASHINGTON — Walmart and Rite Aid Corp. are among the organizations to side with the Generic Pharmaceutical Association (GPhA) in its opposition to the Food and Drug Administration’s proposed rule on prescription generic drug ­labeling that would require manufacturers to change the prescribing information on their products if they receive new safety information, a change which they say would open them to product liability ­lawsuits.

“Walmart was a pioneer in promoting safe, affordable generic medicines for consumers and their families through its groundbreaking $4 generics program and continues to be a leader in ensuring access to lifesaving medicines,” said GPhA president and chief executive officer Ralph Neas. “They lend their voice to a chorus of health care companies concerned that the proposed rule creates a regulatory framework whereby multiple, different labeling — including different warnings — can simultaneously exist in the marketplace for multiple generic versions of a drug.’’

Walmart and Rite Aid added their names to a letter to the FDA signed by 22 health industry groups, raising concerns about the proposed regulation. The signatories called for the FDA to “fully explore the potential unintended consequences that the rule may have on patient access and national health care costs. Permitting labeling changes for generic drugs without FDA approval counters 30 years of law requiring generic and brand medicines to have the same labels.”

The letter also pointed to the impact of the proposed rule on health care system costs, citing a recent study by Matrix Global Advisors. It showed that spending on generic drugs would rise by $4 billion a year (5.4% of generic retail prescription drug spending in 2012). Of this, government health programs would pay $1.5 billion, and private health insurance, $2.5 billion.

Meanwhile, 19 organizations representing disability, patient advocacy and other populations that GPhA notes most rely on access to generic drugs also submitted letters to the FDA raising their concerns.

“Patient advocacy, disability, veterans, minority and provider groups are taking their place at the table and raising serious concerns about the negative impact of the proposed rule,” said Neas. “The number of voices is mounting.’’

Neas noted that because they speak for millions of Americans who rely on generic drugs, “these groups are asking for inclusivity in creating this rule” and that they do not want to be left behind in the FDA decision-making process.

“Patients and health care practitioners must have access to consistent, transparent information in order to best inform treatment decisions and promote safety,” states one letter.