The players' association has rejected Major League Baseball's latest pace-of-play proposal, according to sources.

The rejection increases the likelihood that baseball will unilaterally implement a pitch clock and a limit on mound visits in advance of the 2018 season.

Union executive director Tony Clark and commissioner Rob Manfred are scheduled to meet next week, but a source familiar with the negotiations said the sides remain far apart on the issue and are not optimistic they will reach an agreement through further talks.