I echo my colleague and am only adding to the answer here.
It is not ordinarily legal in Illinois for an employer to prohibit the taking of your lunches. I say ordinarily because the guiding law my not apply to your situation as you operate under a collective bargaining agreement.
The controlling default law is 820 ILCS 140/3 which you can read for yourself here: http://www.ilga.gov/legislation/ilcs/fulltext.asp?DocName=082001400K3
Here is the law in it's entirety as well:
(820 ILCS 140/3) (from Ch. 48, par. 8c)
Sec. 3. Every employer shall permit its employees who are to work for 7 1/2 continuous hours or longer, except those specified in this Section, at least 20 minutes for a meal period beginning no later than 5 hours after the start of the work period.
This Section does not apply to employees for whom meal periods are established through the collective bargaining process.
This Section does not apply to employees who monitor individuals with developmental disabilities or mental illness, or both, and who, in the course of those duties, are required to be on call during an entire 8 hour work period; however, those employees shall be allowed to eat a meal during the 8 hour work period while continuing to monitor those individuals.
(Source: P.A. 88-73.)
Based on the law, if the employee is to work 7 1/2 hours or longer, it would appear that the employee is entitled to at least a 20 minute lunch break.
You have identified yourself as a union member, and while I think it highly unlikely, when you read this law, a specific paragraph states this law does not apply if your meal breaks were established through collective bargaining. Most likely, your union has negotiated for a longer lunch and is most likely even more liberal in terms of a guaranteed lunch break than the Illinois law.
You pay union dues, and a grievance with the union is my recommended course of action as your union already has a relationship with an attorney who can assist if necessary in your situation.
If your collective bargaining agreement does not specify or address meal breaks, than the Illinois law above will govern.
One word of caution. In a suit for damages, you and the others who have had to work through lunch will likely be successful in collecting whatever pay you were owed. However, Illinois is an "at-will-employer" state and unless your union negotiated a policy and procedure that would then govern, it is very easy in Illinois for an employer, Postal Service or otherwise to terminate an employee with no reason being given or owed.
Again, I recommend you go through your union as then you will have a collective action and any union protections that have been negotiated for.
I would also caution you against causing a disruption at your work over this issue. Make sure you ask for your lunch breaks, and work with your union, but in these hard economic times, I advise you to be careful because you might win the battle over lunch and lose the war of your job.
Good luck and be sure to keep all discussions with your supervisor professional, courteous, and hopefully with a witness.
This answer is marginal legal advice and does not constitute an attorney-client relationship. Every client and case is unique. The best advice is to always consult with an attorney. Free legal resources at www.ZippToCourt.com
You are a union member and have representation through your union. An employee who works a full day is entitled to a lunch break. However, whether your employer's refusal to allow you a lunch is legal or not does not resolve your problem which is, as you indicated, that you work hungry. You are entitled to file a grievance, which you have done or are doing. So no, it's not legal and apparently you are following correct procedures through your union.