AT&T, one of the world’s largest telecommunications companies, figures prominently in the annals of antitrust law.

Since the late 19th century, under various names and configurations, the entity once known as Ma Bell has often been targeted by regulators trying to rein in its size and keep it from amassing monopoly power.

Now, AT&T is facing off against the Justice Department again, this time over its proposed $85.4 billion takeover of Time Warner. And although the details are different, the current situation is a reminder of the complicated balancing act the government must strike in regulating ever-changing companies.