Major League Baseball has imposed stricter limits on mound visits by players in an effort to speed up games, but it decided against 20-second pitch clocks for 2018.

After more than a year of negotiations, the Major League Baseball Players Association refused to agree to the changes but also signed an agreement that it will not oppose the rules.

The amendments to the playing rules announced Monday include a general limit of six mound visits per nine-inning game without a pitching change, whether by a manager, coach or player.

Major League Baseball

To assuage players' concerns about sign stealing, MLB will install new telephone lines from dugouts to video replay rooms. MLB said the lines will be monitored, and a person familiar with the decision told The Associated Press all conversations on the lines will be recorded. The person spoke on condition of anonymity because that detail was not announced.

MLB has the right to make playing rules changes absent an agreement with one-year notice, and it made proposals during the 2016-17 offseason for a pitch clock and more restrictions on mound visits.

"I am pleased that we were able to reach an understanding with the players association," commissioner Rob Manfred said in a statement. "My strong preference is to continue to have ongoing dialogue with players on this topic to find mutually acceptable solutions."

Union head Tony Clark noted the sides technically did not reach a deal.

"The focus on mound visits and/or the level of commitment on the other pieces simply didn't focus enough attention on the areas the players wanted to address -- so no agreement was reached," he said in an email to the AP.

"While a number of pitchers will acknowledge that some mound visits are unnecessary, a limitation combined with what the experience has been of late in regard to technologically enhanced sign stealing means that there are concerns about how this will work ... or not work."

Boston Red Sox manager Alex Cora expressed concern that changing signs between a pitcher and catcher without a mound visit can result in a safety issue.

"I understand we want to speed up the game. I get it. We don't want as much dead time during the game," Cora said. "But that's one that's an interesting one because we know what's going on around the league. Everyone is working hard from second base to take an advantage. ... Teams are very aware of switching signs and everything that is going on, and there's a lot of cross-up.

"We'll see how it goes. You call a breaking ball, you throw a fastball at 98 [mph] and the catcher is looking for a breaking ball and he gets hit. We're talking about safety and keeping guys on the field."

Until now, the only restriction on mound visits was that a second visit to the same pitcher during an inning by a manager or coach resulted in an automatic pitching change.

The number of visits by catchers during games has increased in recent years, contributing to the average time of a nine-inning game stretching to a record 3 hours, 5 minutes last season, up from 2:46 in 2005.

Under the new rule, each team would get an additional mound visit without a pitching change for each extra inning. Trips will not count against the limit after an offensive substitution, to check on potential injuries or to clean spikes on wet fields. If a team is out of visits, the plate umpire may give permission for additional trips by the catcher in the event of a cross-up on pitch signals.

As far as discipline regarding mound visits, the umpire is empowered to enforce the rules up to and including ejection from the game, sources told ESPN's Buster Olney. The MLB baseball operations team can also discipline players separately, sources told Olney.

MLB is eliminating the rules guaranteeing eight warm-up pitches before a half-inning in an effort to keep between-inning breaks to 2 minutes, 5 seconds for most games, 2:25 for regular-season games on national television and 2:55 for tiebreaker and postseason games. There are exceptions relating to injury and if the pitcher or catcher finishes the previous half-inning on base, at bat or on deck.

ESPN's Scott Lauber and The Associated Press contributed to this report.