The Senate Judiciary Committee is taking testimony on the measure Tuesday.
And advocates and critics of same-sex marriage have promised to be at the Statehouse in force.
Meantime, more than 125 professors from 48 law schools around the country have signed a letter saying New Jersey's civil union law cannot be fixed.
The professors, including New Jersey former Public Advocate Ron Chen, say the law granting gay couples the benefits of marriage without the title will never be equal to the right to marry.
The letter was sent to Gov. Chris Christie and the Legislature.
A gay marriage bill was defeated in the Senate two years ago. But Senate President Stephen Sweeney has since had a change of heart and is now sponsoring the legislation.
The bill never came up for a vote in the Assembly.
Gov. Chris Christie is no fan of gay marriage. But the governor says he will look at the bill if it gains momentum.
The hearing comes one day after the Republican governor nominated an openly gay black man to the state Supreme Court.
