OAKLAND -- BART and its unions were back at the negotiating table Tuesday just days before their deadline -- and for the second day in a row gave no warning of a possible walkout.

And, for riders awaiting word on whether trains will continue running, no news may be good news.

Late Monday, labor unions said they would not issue a customary 72-hour notice of a strike for Friday morning.

This comes after the unions -- who have vowed to alert the public before walking out -- issued three-day notices before a July shutdown and a planned August walkout that was eventually averted.

"It's definitely a positive sign," said Harley Shaiken, a UC Berkeley professor who specializes in labor issues. If the unions were to strike without notice, as Boston school bus drivers did on Tuesday, it "would clearly anger a lot of commuters. I suspect the union is well aware of that."

Still, the strike notice is not required, and unions could still shut down BART trains after the 60-day cooling-off period ordered by Gov. Jerry Brown expires at 11:59 p.m. on Thursday. The BART Board of Directors canceled a tentative meeting that had been scheduled for Wednesday evening in case a deal is reached, making it clear the talks would go down to the wire Thursday as both sides had long suspected.

Several hundred workers rallied in Oakland on Tuesday, chanting slogans such as "stand up with the workers, down with the greed," and holding signs advocating for a better deal than management is offering.

"We've been ready to negotiate for months and as usual we get dragged along to the last second, to the last minute. We are fed up with that," said Sal Cruz, a 10-year train controller at BART, one of several workers to speak at the union rally.

After making progress last week, it's unclear how the most recent talks are coming along as mediators this week issued a gag order preventing negotiators from reporting news from the bargaining table. Both sides are honoring the request to keep quiet for the first time since talks began more than six months ago -- a sign, experts think, indicating that they are trading proposals and working toward a compromise.

"This time around they're both hunkered down," Shaiken said.

Last week, the latest offers showed the two sides were about $1,500 apart in base pay increases per year, and were also arguing over the level of bonuses that workers would receive in good financial times.

Staff writer Kristin J. Bender contributed to this report. Contact Mike Rosenberg at 408-920-5705. Follow him at twitter.com/RosenbergMerc.