Aetna Inc. and 19 other companies are being urged to disclose their contributions to independent political organizations by investors including unions and state pension funds with $922 billion in assets.

The New York State Common Retirement Fund and the UAW Retiree Medical Benefits Trust are among 25 investors who demanded to know how Aetna, the third-biggest U.S. health insurer, is wielding its political influence and giving money to advocacy groups such as the American Action Network, an organization opposed to President Barack Obama's policies.

"Recent reports that the company accidentally disclosed over $7 million in donations to the American Action Network and the U.S. Chamber of Commerce suggest that the company continues to obscure the full extent of its spending," the group wrote in an Aug. 7 letter to Aetna's board. The shareholders also questioned whether the Hartford, Connecticut-based company was failing to report payments to groups that operate outside of campaign disclosure laws.