A bill aimed at keeping Japan's pension system sustainable in the face of a graying and shrinking population passed in the House of Representatives Tuesday amid fierce protests from opposition parties.

The ruling coalition of the Liberal Democratic Party and Komeito are aiming to introduce the bill in the Upper House on Friday at the latest so it can be put to a plenary vote for enactment by Dec. 14, the end of an extension to the current extraordinary Diet session.

The governing parties described the bill as essential to softening the impact of demographic change on the pension system, while the opposition claimed it would threaten the livelihoods of those already struggling to get by on pensions.