A day of negotiating brought Major League Baseball and the MLB Players Association no closer to a new collective bargaining agreement, according to sources familiar with the talks.

The sides met in Irving, Texas, on Tuesday, one day before the current agreement is set to expire at 11:59 p.m. ET Wednesday.

Though the sides have tweaked their proposals in recent days, the core economic issues are still the major road block to a new deal. The players want free agency after five years or 29.5 years of age, whichever comes first, while beginning the arbitration process after two seasons instead of three.

Owners won't agree to such a massive overhaul of the system, according to a person familiar with the league's thinking. Both free agency after six years and arbitration after three seasons have been tenets of the economic process in baseball for decades.

On Tuesday, players added potential revenue-generating ideas, such as allowing advertising patches on jerseys and a 12-team postseason, to their offer. But they also asked for the luxury-tax threshold to be raised to $240 million. It was $210 million last season.

To accommodate the playoff grid in a 12-team postseason, the union offered up each league realigning to two divisions, one with eight teams and one with seven.

The league wasn't moved by any of the proposals, which still include changes to free agency, arbitration and revenue sharing among the clubs.

Last week, the league tweaked its own offer, adding an NBA-style draft lottery to its proposal as well as the elimination of draft pick compensation. Previously, the league proposed a 14-team postseason while agreeing to free agency for all players at 29.5 years old. It also offered to eliminate arbitration and instead use a formula -- FWAR in this case -- to determine salaries for players who normally would be eligible for arbitration.

The impasse is likely to lead the owners to lock out the players at midnight on Wednesday. It's not a mandatory move, as the sides can keep negotiating under the old CBA rules if they desire, but the league insists it's the best route to instill a sense of urgency in the process. The owners don't want a lockout viewed as punitive but just part of the process.

The players won't lose paychecks until the start of the regular season, so they might view the lockout as less risky than an in-season work stoppage would be. If a stoppage occurs, there will be no contact between teams and free agents or players on their 40-man rosters. In fact, team personnel aren't allowed to speak publicly about players as it pertains to their game on the field or in any manner.

The sides will meet again on Wednesday with less than 24 hours until the old CBA expires.