Negotiations between the NBA owners and players have been contentious at times, but now they are turning downright nasty.

Following another failed round of talks Saturday aimed at ending the four-month old lockout, NBA commissioner David Stern made his boldest statement yet when he issued an ultimatum to the players. The NBA said it offered players up to 51 percent of basketball-related income — and if they don't accept the offer by Wednesday, the percentage will drop to 47 percent.

The players are said to be willing to drop their previous demands of receiving 52.5 percent of the revenue split to 51 percent, but in doing so they want certain luxury cap concessions. The owners aren't hearing it. They want a more favorable revenue split and a stricter salary cap system.

"We hope that this juxtaposition will cause the union to assess its position and accept the deal," Stern said at a news conference early Sunday morning.

The players’ union, led by president Derek Fisher and executive director Billy Hunter, broke from the meeting, saying Stern’s offer was unacceptable. They continued to say so Sunday as they began taking steps for a mandatory convening of all 30 team representatives Tuesday in New York, according to reports. Apparently that will be the point made during Tuesday’s gathering.

This could get even more interesting now as the movement by a faction of star players, including Boston’s Paul Pierce, to decertify the union continues to take shape. Sources confirmed to ESPN.com that a third conference call is planned for Monday to discuss decertification.

The players will need to gather at least 200 signatures from the approximately 450 members to file a petition with the National Labor Relations Board to call a formal decertification vote. The players would then be putting the owners on the clock because they would have 45 days after the petition is filed before the case is heard.

A move for decertification at this point is risky for both sides because owners will then face a costly lawsuit, and for the players it will almost certainly mean the cancellation of the entire 2011-12 season while this ordeal plays out in a court room.

Contact Terrance Harris at terrancefharris@gmail.com or follow him on Twitter @Terranceharris

 (Photo: Neilson Barnard/Getty Images)