The Major League Baseball Players Association has offered more tweaks to its latest proposals, but again there was no real progress on the biggest issues holding up a new collective bargaining agreement.

The tweaks came Thursday, the fourth straight day of negotiations.

The league said Wednesday that it will begin canceling regular-season games if the sides can't reach an agreement by Monday. 

They met for under four hours at Roger Dean Stadium on Thursday with no apparent progress on issues such as competitive balance tax, minimum salary structure, salary arbitration, revenue sharing or a pre-arbitration bonus pool.