I submitted a job application for a promotion 11 months ago, and was told that due to personnel needs the posting was postponed indefinetly. 9 months ago I was moved into that department and 6 months ago began performing all the duties of the job i bid on. upon inquiring on my promotion I was told that the posting i bid on was no longer valid and I continue to work at the lower rate of pay. Is there any law that covers this type of situation, or is it simply employer discression?

This would be at the discretion of the employer. If you are employed under a collective bargaining agreement, I'd suggest speaking with your union rep for guidance.

Generally speaking an employer is not required by law to offer a pay raise or promotion because an employee has been given additional responsibilities. It's not uncommon for companies to redefine jobs. Often these redefinitions will result in changes of responsibilities to affected staffers. It's unfortunate that you now have additional work; but it's not unlawful. Be glad that you have a position where you are trusted by your boss. This will boad well for future chances at advancement. Keep up the good work. Your star will shine. Just be patient.