SAO PAULO - Mexico's incoming president Enrique Pena Nieto on Wednesday raised pressure on his Institutional Revolutionary Party (PRI) to back a labor reform proposed by the outgoing administration, saying he was optimistic Congress would pass it.

The draft bill put forward this month is viewed as a litmus test of cooperation between the centrist PRI and President Felipe Calderon's conservatives. The lower house of Congress has 11 more days to either approve or reject it .

The reform aims to soften Mexico's antiquated labor laws and force its trade unions to become more transparent, which has raised the hackles of the PRI's powerful union base.