NEW YORK — Major League Baseball and its players agreed to an unprecedented early start to contract bargaining, a move sparked by union anger that raised the possibility of a return to work stoppages that marred the sport in the late 20th century.

MLB and the union announced modest rule changes Thursday.

Players have been furious at slow free-agent markets during the first two offseasons of the collective bargaining agreement set to expire Dec. 1, 2021. The agreement increased the level of the luxury tax and prompted more teams to jettison veterans in favor of rebuilding with youth. None of the previous 11 collective bargaining agreements dating to 1966 was overhauled in mid-agreement, except for limited areas defined by the sides when the deal was signed.

“It remains to be seen what the union’s going to ask for, what we’re going to ask for and whether we reach an agreement,” deputy commissioner Dan Halem said. “It’s a positive sign we were able to reach an agreement with the union on rule changes and hopefully we can build on that.”

Ordinarily, the sides would have started negotiations in March 2021. The union proposed major economic changes this offseason that management refused to consider, such as expanding the DH to the National League, addressing service-time rules that affect eligibility to free agency and salary arbitration. Also, adding provisions to the amateur draft that would make it harder to accumulate high draft picks over several seasons. As part of the deal on rule changes designed to speed the pace of play, management agreed to broader talks.

Baseball had eight work stoppages from 1972-95 but has reached four straight deals without interrupting play. While there is no deadline, as a practical matter the sides would have to agree to major economic changes before free-agent negotiations start, on the sixth day following the World Series.

TIGERS: Right-hander Michael Fulmer will not pitch in games in the near future, focusing on lower-body mechanics.

“He took a step back to refine his lower-body mechanics,” Detroit Manager Ron Gardenhire said. “We have no timetable when he’s going to get back on the mound.”

Gardenhire declined to provide additional details.

YANKEES: Luis Cessa dropped his ERA to 0.69 with four scoreless innings for the Yankees in a 1-1 tie with the Blue Jays at Dunedin, Florida.