Star Trek The Original Series Rewatch: "A Taste of Armageddon"
Captain’s log. The Enterprise has been hailing the people of the Eminiar star system. Ambassador Robert Fox is on board, as the Federation is hoping to open up diplomatic relations, but there’s been no response. Uhura finally gets an answer: a code 710, which is a message that there is conflict and to stay away or risk being damaged. Fox orders Kirk to disobey the 710 despite the very real risk to the Enterprise, so Kirk sighs and orders yellow alert and goes in. Fox’s orders are to open diplomatic relations with these planets so the Federation can establish a needed port there.
Source: tor.com