It was called the Economic Opportunity Act, a measure intended to kick-start the sputtering post-recession economy in New Jersey, particularly in its struggling cities. The state would award lucrative tax breaks to businesses if they moved to New Jersey or remained in the state, creating and retaining jobs.

But before the bill was approved by the Legislature, a series of changes were made to its language in June 2013 that were intended to grant specific companies hundreds of millions of dollars in additional tax breaks, with no public disclosure, according to interviews and documents obtained by The New York Times.

Many of the last-minute changes to drafts of the bill were made by a real estate lawyer, Kevin D. Sheehan, whose influential law firm has close ties to Democratic politicians and legislative leaders in New Jersey.

Mr. Sheehan was allowed by lawmakers to edit drafts of the bill in ways that opened up sizable tax breaks to his firm’s clients, according to a marked up copy of the legislation obtained by The Times, which identifies Mr. Sheehan’s changes.