My company has been withholding expenses, along with other payments, during the month of December for the entire of my tenure with them. This has caused me financial distress. Is this a general accepted practice or a form of "cooking the books"? Do I have any recourse for these practices?

Many companies due this because of budgeting. It may be there practice, in that case I doubt there is anything you can do.

Budgeting?

I would say it would be a cash flow issue.

That is, assuming I understood your question. From my understanding, you paid money and submitted a claim to your company for reimbursement and they have yet to pay you?

My guess is simple cash flow issues for the company. Yes, they shouldn't be taking so long, but what are you going to do? Sue them? That is a waste of time and money since they will probably pay you within a month…

What you could do is not pay for anything anymore, and instead insist on cash upfront due to this.