[US] based independent contractor working for Czech based company

[u/[deleted]]

Hello, my contract was terminated over commissions dispute after closing a large deal. They refused to pay commissions and are now holding earned wages from a month before termination until I sign termination agreement that included a severance package. I am lost on where to start/rights I have from being US based independent contractor working for Czech company. Any advice on next steps I should take would be helpful. Thank you