Wal-Mart Stores has drawn fresh criticism from shareholder-advisory firms over topics ranging from executive compensation to its handling of a foreign-bribery scandal.

Institutional Shareholder Services and Glass Lewis & Co. have chided Wal-Mart in reports released over the past week, saying there are unanswered questions about probes into possible violations of the Foreign Corrupt Practices Act in Mexico, Brazil, China and India.

Institutional Shareholder Services also recommended rejecting Wal-Mart's executive compensation in an advisory vote at a shareholder meeting on June 6.

Wal-Mart's founding family controls more than half its outstanding shares, so the recommendations are unlikely to affect the outcome of proposals at its investor meeting. Still, the criticism is lending support to groups lobbying for changes.

The probe into alleged foreign corruption "is an ongoing investigation, and we're cooperating fully with the Department of Justice," said Randy Hargrove, a spokesman for Wal-Mart. "We don't have a timeline for when the investigation will be completed, but we haven't waited to act. The board has authorized whatever resources are necessary to get to the bottom of the matter."

On the question of pay, Hargrove said Institutional Shareholder's own analysis shows the company's compensation aligns with its performance.

"Wal-Mart operates a complex business, and it's important that we offer competitive pay to attract the right talent," he said.