I'm afraid I can't post a usable link since this is only in the WSJ at this point.

Tesla Inc.’s TSLA 0.96% tumultuous year has fueled concern among some of its suppliers about the auto maker’s financial strength after production of the Model 3 car drained some of its cash, according to industry executives and documents.

A recent survey sent privately by a well-regarded automotive supplier association to top executives found that 18 of 22 respondents believe that Tesla is now a financial risk to their companies, according to the document reviewed by The Wall Street Journal.

Separately, several suppliers in interviews said Tesla has tried to stretch out payments or asked for significant cash back. And in some cases, public records show, small suppliers over the past several months have claimed they failed to get paid for services supplied to Tesla.

Tesla has improved its on-time payments to production-related suppliers to about 95% from 90% last year, according to people familiar with the matter. For nonproduction suppliers, Tesla is paying on time about 80% of the time, the people said.
It is not at all unusual for companies to ask suppliers for year over year price reductions---but asking for actual cash paybacks is a new one on me.