The American Federation of Teachers Massachusetts scrapped plans to fight legislation that would reduce the role of seniority in teacher staffing decisions and instead will remain neutral on the issue, the state’s second-largest teachers union announced Wednesday.

The legislation, unveiled earlier this month, is on the fast track to secure approval in the state Legislature and aims to stave off an emotionally divisive ballot question that called for more sweeping changes. The teachers federation had initially promised an aggressive fight against what it called “extreme legislation.’’