Independent investors are taking aim at Walmart’s tight-knit culture, which they blame for a corruption scandal that is threatening to spoil the company’s 50th birthday party tomorrow.

“Walmart is controlled by the Walton family and other insiders steeped in the ‘Walmart way’,” said John Liu, the New York City comptroller who oversees five public pension funds that will vote against certain Walmart directors at the retailer’s 50th annual meeting in Arkansas tomorrow. “Outside shareowners need strong, independent directors willing to challenge this dominant culture when necessary to protect long-term shareowner value.”

Walmart, the folksy and penny-pinching business that grew into the world’s biggest retailer by sales, has been accused of paying bribes to accelerate its expansion in Mexico and then hushing up the practice.