Matson's largest shareholder is strengthening its position in the Jones Act boxship player.

According to a Securities and Exchange Commission filing made on Thursday, investment giant BlackRock upped its stake in the Hawaiian company to 15.1% by buying more than half a million shares.

BlackRock now owns 6.4 million shares in Matson, up from 5.8 million.

The New York-based firm is the largest shareholder by more than two million shares, ahead of Vanguard, which