WASHINGTON � With a series of recent high-stakes cases, the Federal Trade Commission has become increasingly aggressive in its pursuit of unfair or anti-competitive behavior by patent holders, according to patent litigators and others, who are now watching to see if the agency will step into a multibillion-dollar fight that could affect the nation’s federally mandated conversion to digital television.

The American Antitrust Institute (AAI), a Washington-based advocacy group, recently filed a petition with the FTC asking it to investigate alleged antitrust patent “holdup” by Rembrandt Technology L.P., a patent holding and licensing company based in Bala Cynwyd, Pa.