ISS endorses most of activist Ancora's nominees for Norfolk Southern board

Influential proxy advisory firm ISS recommended on Tuesday that Norfolk Southern shareholders support five of activist Ancora's seven board nominees, withholding an endorsement from CEO pick Jim Barber but describing him as a "credible director and CEO candidate nonetheless."

ISS' endorsement, in a report viewed by CNBC, comes one day after Glass Lewis endorsed most of activist investor's slate of nominees and days after two unions came out in support of Ancora's proposed management team.

The proxy advisor recommended shareholders support CEO Alan Shaw's reelection to the board over Barber, but in a rebuke of NSC's existing governance, it said shareholders should not support current board chair Amy Miles.

Ancora is seeking to oust both current CEO Shaw and newly appointed COO John Orr. The activist holds Shaw accountable for NSC's historic underperformance relative to peers, and for a disastrous derailment in East Palestine, Ohio, just a few months into his tenure.

Glass Lewis, the other influential proxy advisory firm, said shareholders should support Barber over Shaw in its recommendation Monday. While neither endorsement suggests giving Ancora full control of the board, both provide the dissident with a clear mandate to implement change.

Investors, especially passive index-fund giants like Vanguard and BlackRock, pay close attention to proxy advisors' recommendations when deciding how to vote their millions of shares. The top three shareholders at Norfolk Southern control more than 16% of shares outstanding.

ISS said in its report that it was clear "that the dissident has presented a balanced slate consisting of qualified nominees, and has generally targeted the appropriate management nominees."

ISS recommends shareholders support Ancora nominees William Clyburn, Sameh Fahmy, Gilbert Lamphere, Allison Landry and John Kasich.

The proxy advisor said that Norfolk Southern's governance problems were "most evident" in the board's failure to communicate with investors and prioritize their "best interests."

"As board chair, Amy Miles arguably bears the most responsibility for this state of affairs," ISS' report read.

Norfolk Southern has taken steps to address investor concerns, including appointing Orr as COO and adding two new directors, former Sen. Heidi Heitkamp and former Delta CEO Richard Anderson. ISS endorsed Anderson's election but said shareholders should not support Heitkamp.

"There is no evidence suggesting that Heitkamp is in any way unfit to serve, but dissident nominee John Kasich has comparable regulatory and administrative experience," the ISS report said, mentioning the latter's "proven ability" to foster compromise.

WATCH: CNBC's full interview with NSC CEO Shaw on activist campaign