The IRS itself, in its regulations and rulings, has held that a 501(c)(4) can provide a substantial (but unquantified) private benefit to its members so long as its primary activity is promoting the common good, says George Washington University law professor Miriam Galston.

FORBES: Magazine Article

Central YMCA, a charity promoting the benefits of physical activity on mental health, runs exercise referral programmes.

BBC: Depressed 'denied exercise help'

REV, for example, can trigger the activity of cancer-promoting genes and, as a consequence, it causes a wide range of gallinaceous tumours.

ECONOMIST: Foulpox

Groups granted tax-exempt status under section 501(c)(4) of the tax code are allowed to engage in some political activity, but their primary focus is supposed to be promoting social welfare.

WSJ: Chiefs at IRS Knew of Targeting

Tax-exempt social-welfare groups organized under section 501(c)(4) of the Internal Revenue Code are allowed to engage in some political activity, but the primary focus of their efforts must remain promoting social welfare.

WSJ: Wider Problems Found at IRS

Promoting social welfare can include lobbying and advocacy for issues and legislation, but not outright political campaign activity.

WSJ: IRS Scrutiny Was Deeper Than Thought