(Bloomberg) -- Billionaire investor Carl Icahn is increasing his offer for Southwest Gas Holdings Inc., the latest step in his months-long campaign to take over the utility. 

Icahn’s IEP Utility Holdings LLC is offering $82.50 a share, up from the prior offer of $75, according to a statement Monday. 

Southwest Gas shares surged as much as 10%, to $79.92 before the start of regular trading in New York.

The activist, who owns about 5% of Southwest Gas, has been pushing to take it over since October, when the company defied his objections and moved forward with plans to buy Questar Pipelines from Dominion Energy Inc. for about $2 billion.

The board of Southwest Gas unanimously rejected Icahn $75-per-share offer, arguing it undervalues the company and isn’t in the best interest of shareholders. 

Earlier this month, Southwest Gas said it plans to spin off a construction business that Icahn had pushed the utility to sell. The activist criticized the move, saying it was a “vague promise” and “not necessarily a step in the right direction.”

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