Updated

Representatives for Major League Baseball and the players union are in agreement that wild-card expansion should take the form of a one-game knockout round, a source confirmed to FOXSports.com Saturday.

The parties are currently negotiating a new collective bargaining agreement, with the current one set to expire in December. The deal could be in place by the end of this year's World Series, but the expanded postseason -- from four teams in each league to five -- is more likely to take effect in 2013 than 2012.

The New York Post first reported the development Saturday morning.

The union is not inclined to add the extra wild-card round in 2012 unless the leagues are balanced at 15 teams each, one source told FOXSports.com.

The players have insisted on evening the number of teams in each league so that the competition for those wild-card spots is even. This is the so-called "15-and-15" concept, with the Houston Astros being the most likely team to move from the National League to the American League.

For the time being, the biggest hangup in talks remains the owners' desire for slotting players in the amateur draft, one source said, but other issues remain.

The two sides are "very far apart" on the luxury tax, including what the rates and new thresholds should be. There are likely to be penalties for violating the revenue-sharing plan for teams that do not spend the way fellow owners think they should. But there will be no tax for violating a minimum payroll level, a source said.