Christie has given a team of advisers until Friday to come up with financing options that could keep the $9 billion project on track.
The governor killed the tunnel because of cost overruns. But Christie agreed to reconsider at U.S. Transportation Secretary Ray LaHood's urging. The federal government is kicking in $3 billion to the largest public works project under way in America.
New Jersey's share is $2.7 billion, with the state being responsible for overruns. Christie says overruns could add $2 to $5 billion to the price tag. Sen. Frank Lautenberg says the number is significantly lower.
The tunnel would double rail capacity between New Jersey and New York.
Last week, results of a new study found the rail tunnel would cut the commuting time between New Jersey and New York City and would increase NJ Transit's on-time performance and drive economic growth.
New Jersey Gov. Chris Christie killed the project because of cost overruns.
The Democrat has met with an undisclosed major financial firm to discuss private funding to keep the project on track.
More than half a billion dollars have been spent so far.