A Minnetonka DFL senator broke with her party Thursday to take on some of its most powerful allies with a measure that could end the long-standing practice of teacher tenure, which makes job seniority the prime consideration during layoffs.

Eliminating so-called last-in, first-out protections has been a goal of Republicans, but opposed by many DFLers, who count the teachers’ union Education Minnesota among its staunchest allies and who say there is value in keeping experienced teachers in the system.

Sen. Terri Bonoff said Thursday that “It is my belief that really in every profession merit ought to be what gets someone hired, promoted or kept. I believe especially in a profession where our teachers play such an important role in shaping the lives of our young people that we want to make sure the very best teachers are in every classroom.”

Bonoff, who has made education a key concern during her four terms at the Legislature, has attracted some bipartisan support, with Republican Senators Branden Petersen, of Andover, and Eric Pratt, of Prior Lake, signed on as cosponsors. Republicans in the House have already introduced a bill that would end teacher seniority and take measures to close the achievement gap between white and minority students, sponsored by Rep. Jenifer Loon of Eden Prairie.

When Republicans last controlled the Legislature in 2012 they pushed through a measure that would have eliminated so-called last-in, first-out practices, arguing that they hurt student achievement. DFL Gov. Mark Dayton vetoed the bill — which Bonoff supported — saying it was vague and premature in the absence of a well-developed, objective evaluation system.

The landscaped has changed since then. The teacher evaluation system that was then in the beginning stages now has been implemented statewide, giving school districts more data on teachers’ effectiveness in the classroom. Under the state evaluation law, 35 percent of a teacher’s evaluation must gauge student achievement as measured by tests.

“School districts have the tools, they have the information available to implement whatever improvements they think are necessary in their system,” Dayton said in an interview earlier this month. “We’re on that track, and if the Legislature wants to review the track and look at it, then that’s fine.”

A spokesman for the governor said Dayton has not yet reviewed Bonoff’s bill.

Like Dayton, Republicans are homing in on education as a top priority during the current legislative session.

Education Minnesota, the state’s union representing 70,000 educators, criticized efforts by lawmakers to end the teacher seniority protections.

“Constantly improving the quality of teaching… is a goal Education Minnesota shares with many lawmakers and parents, but this relentless focus on layoffs won’t help any teacher get better,” Denise Specht, president of the union, said in a statement.

Specht said that lawmakers instead should designate more money — beyond the $75 million the state already has committed — to fully fund the evaluation process. Some school districts lack the resources, staff and expertise to carry out the new requirement. The teachers’ union is lobbying for a legislative fix, Specht said.

“If the Legislature really wants to improve teaching quality, it should fully fund the 2011 Teacher Development and Evaluation law and permit districts to use their local plans,” she said. “With so many serious issues facing our schools, it’s disappointing that some lawmakers want to spend their time micromanaging personnel policies in Minnesota schools.”

Bonoff said her bill is not an attack on teachers as critics have contended in the past.

“When I carry legislation like this, it’s in no way not honoring the role [teachers] have played in our society and in our community,” Bonoff said. “They have quite a challenge before them.”