Joe should see a lawyer about a wrongful termination lawsuit.
The Bill Emerson Good Samaritan Food Donation Act (pdf) brought to law in 1996 shields most liability for people donating food exactly like he did.
This may have been a knee-jerk reaction from the employer incorrectly assuming they could be liable if someone got sick. Though its also possible they've been looking for a reason to dismiss a long time employee to replace him with a cheaper one. Corporate ownership makes me leans towards the latter.