It's my understanding that if you have any options or short sales in your account that the entire account becomes collateral, even if you have a positive cash balance. That means your broker can loan out your shares. This could vary depending upon the specific agreements with different accounts and different brokerages, but I believe it holds true extensively, across the board. It's the norm.
If you don't want TSLA shares held in your account to be loaned to shorts without you knowing, it's a good idea to put them under a limit-sell order at a high price (mine is currently at $2200) to prevent your broker from loaning them out for short selling purposes.
if you have a margin account, and are using margin to support any of the positions within your portfolio, all positions are subject to liquidation/loan
brokers don’t do security by security margin. meaning i bought my tesla with cash but used broker margin to buy calls, or another stock, (security B)
therefore if security B takes a dump, and your maintenance requirement is exceeding your net liquidation value (your portfolio value), you are subject to getting not only security B liquidated, but also TSLA.
the outstanding GTC will not prevent this.
as far as loaning out your position, they can only loan out what is owned in excess of what you paid for with your money.
so, in general;
if i opened an account with 50k cash and bought 50k of tsla, and i do not opt into sec lending, they can’t touch those shares. they can go to 0, my buying power will decrease with the price and value of the position, but they can’t go negative, so i won’t owe broker anything.
if i use the 50k worth tesla as leverage to buy 10k worth of security B, i’m now on margin.
that 10k loan is subject to liquidation and/or loan to street. so in that sense, i agree with you.
as the two securities fluctuate in value, so does the the margin requirement against the net liquidation value of the acct.
if during the duration of ownership of those two securities, the broker finds it can make money off the 10k loaned to you by loaning out tsla or security b (but only up to 10k loan value), they will most likely do so.
should things go haywire with one or both securities, they broker will liquidate whatever it can as fast as it can to recoup it’s 10k that it loaned to you.
i guess my point is, i don’t see gtc preventing either of those two scenarios, because once you get into margin on security B, the broker can do what it wants with that 10k.
they can’t, by rule, do anything with fully paid shares. they are segregated and reported daily to DTCC, and subject to audit by finra, exchanges, sec, etc