Can I legally hold a businesses possessions until I recieve payment for my services all ready rendered?

[nooner]

I did graphic design, among other things, for a company for free with the understanding for 15% partnership into the company. They recently told me they changed their mind and that I would not be a partner. I gave them the amount and hours of what I did design wise and told them I want a contract written saying they will pay me the full amount within a year. They're dragging their feet, and the same time they are asking for a bunch of shirts (with my design on them that they haven't paid for yet). So my question is, will I be in legal trouble if I do not hand these over until we have worked out an agreement and have it signed?

They want to some out tomorrow.

Thanks in advance.

[nooner]

I need to add that they paid to have the shirts made. Just didn't pay for my service. Worse yet they trademarked my logos I created for them.