Transactions between related Proprietorship Firms

I am having two proprietorship firms - one is under my name and another one under my HUF name in which I am karta. Both are of course under different PAN Nos and GST nos. One of the firms is under Audit in the current Assessment year, the other one is not. 

Are transactions allowed between these two firms and if we do sale purchase between these two firms will there be any issue in Income tax audits and GST Audit?