From their Twitter
Under the new tentative agreements the average all-in hourly compensation for UAW autoworkers, meaning benefits plus pay, is estimated at $88-89/hr.
At Tesla that number is just $45/hr.
That's the difference a union can make.
Tesla has of course been viciously anti-union and, when workers show signs of unionizing, seek to quickly smother said efforts. Earlier this year they fired 30 workers in Buffalo for attempting to organize their workplace; an NLRB complaint has been filed on those workers' behalf by Tesla Workers United. Elon Musk has also been repeatedly reprimanded by the NLRB for anti-union tweets, Tesla's efforts to prevent public support of any union, and what CNN describes as "interrogating employees and disciplining or otherwise discriminating against employees because they support unionizing."