The move stems from ALEC's support for so-called stand your ground laws that allow citizens to shoot other civilians if they believe they are endangered.
Such a defense has been used by George Zimmerman, who shas been charged with second-degree murder in the death Trayvon Martin, 17, in Sanford, Fla., on Feb. 26.
So far, corporate members including Coca-Cola (NYSE: KO), PepsiCo (NYSE: PEP) and Kraft Foods (NYSE: KFT) have quit ALEC. In response, the group on Wednesday denounced coordinated intimidation against its members.
The Washington, D.C.-based business group says it aims to connect state legislators with other state legislators, and companies join because they're more interested in solutions than in rhetoric.
Credo, a liberal activist group, said it's already collected more than 100,000 signatures to urge Dallas-based AT&T to quit. Besides supporting stand your ground, Credo and another group, Color of Change, said AT&T had given ALEC more than $150,000 to sponsor state voter identification laws, which they charge are intended to suppress minority and other pro-Democratic voting.
Common Cause, the public interest lobby founded by John W. Gardner, the secretary of health, education and welfare under President Lyndon B. Johnson, is also involved in the anti-ALEC activity.
Other corporate members getting complaints include Johnson & Johnson (NYSE: JNJ), McDonald's and State Farm.
ALEC's board is top-heavy with conservative Republicans. Its chairman is Rep. Dave Frizzell, R-Ind. Its board of scholars includes Arthur Laffer, the inventor of the Laffer curve in economics, as well as Stephen Moore, a former president of the Club for Growth, which backs Republican candidates.
AT&T, McDonald's and State Farm had no comment. Shares of AT&T rose 32 cents to $30.45, while McDonald's shares rose 89 cents to $98.56.