Shareholder activists targeting Exxon Mobil Corp's climate policies stepped up a campaign to split the chairman and chief executive's roles ahead of the oil major's shareholder meeting on Wednesday.

Unlike European rivals, Exxon faces little government pressure to curb greenhouse emissions or strike deals with climate activists. Under CEO Darren Woods, Exxon blocked six climate resolutions from this year's ballot, encouraging activists to seek the split.

"We have done a lot of one-on-one conversations," said Liz Gordon, executive director for corporate governance at the New York State Comptroller's office, one of several groups co-sponsoring the independent chairman proposal.

"There's a lot of concern about the company and its direction," she said, declining to predict the outcome of the vote. Influential proxy advisor Institutional Shareholder Services this year recommended a vote again the measure.

Exxon has taken steps to bolster its defenses by granting its lead director increased authority to pre-review board agendas and to meet with top shareholders. The proposal last year received nearly 41% of the vote, up from 38.7% in 2018. 

The company has declined to comment on the efforts, but pointed to filings that note shareholders "derive significant benefits" from the combined roles under Woods.

Top Exxon holders' Vanguard Group, BlackRock Inc and State Street Corp also declined to comment on how they plan to vote on the measure or climate-related proposals on the proxy. The three combined own about 20% of Exxon shares.

BlackRock this year signed on to the Climate Action 100+ investor group seeking carbon emissions curbs. 

"BlackRock faces ridicule if it used its vote to undermine Climate 100 backed proposals, and were satisfied with largely cosmetic changes to the lead director's role at Exxon," said Eli Kasargod-Staub, executive director at advocacy group Majority Action.

(Reporting by Jennifer Hiller in Houston; Editing by Bernadette Baum) ((Jennifer.Hiller@thomsonreuters.com; +1 713 210 8538;))