A staunch critic of President Gloria Macapagal Arroyo, his imprisonment in 2006 and 2007 on disputed charges of rebellion and sedition drew international attention.

He was a member of 13th Congress of the Philippines with the Anakpawis ("Toiling Masses") party-list and former chair of Kilusang Mayo Uno (KMU), a militant and progressive labor movement.

Osang delivered his speeches at rallies, and eventually did volunteer work at the Task Force Detainees of the Philippines.

[4] Beltran also drew support from Keith Locke, MP, Foreign Affairs Critic of the Green Party of New Zealand.

"[6][7] Beltran was hurt in a vehicular accident in October 2007 in Intramuros, Manila, when his Toyota Hi-Ace van was rammed by a Ford Everest sports utility vehicle.

Beltran was a cabbie by day and University of the Philippines’ Asian Labor Education Center student by night.

He sustained severe head injuries and was declared dead at 11:48 a.m. by attending physicians at the Far Eastern University hospital,[13] aged 75.