The Liberals began voluntarily posting their expenses last fall, through their party website.
The Conservatives followed suit.
However, the NDP has refused until now to go along, arguing that self-policing by parties of their MPs' expenses was little more than a stunt.
New Democrats say the latest Liberal motion is a partial recognition of their position that disclosure of expenses needs to be complete, standardized and independently verifiable.
The NDP had hoped to move an amendment to the Liberal motion, which would have authorized auditor general Michael Ferguson to audit MPs' expenses - as he is currently doing with senators' expenses.
However, a prior Conservative amendment made it procedurally impossible for the NDP to proceed.
Peter Julian, the NDP's caucus chair, said there's some suspicion that the Conservatives and Liberals conspired behind the scenes to ensure that the auditor general doesn't get the power to audit MPs' expenses.
However, earlier this week, Liberals and New Democrats supported Green party Leader Elizabeth May's attempt to win unanimous consent for a motion authorizing the auditor general to examine MPs' spending habits.
The Conservatives denied unanimous consent.