Tirar línea, soltar línea, recibir línea: to throw the line, to release the line, to receive the line. The Diccionario del español de México of El Colegio de México defines the popular expressions as telling someone how to behave or which guidelines to follow, or listening to such guidelines and obeying them.
The dictionary gives two examples. “El director general nos tiró línea sobre qué hacer en caso de huelga” (The director general gave us the line on what to do in case of a strike). “Estaban ahí nomás, esperando recibir línea del diputado” (They were just standing there, waiting to receive the line from the deputy).