The Democrat-controlled legislature passed the measure on Tuesday, but Gov. Janet Mills, a Democrat running for Senate, has yet to say whether she will sign it.
Analilia Mejia, a progressive Democrat, is competing on Thursday in New Jersey against Joe Hathaway, a Republican who has tried to distance himself from President Trump.
An effort to privatize the facility is a key test of whether Kyiv can overcome concerns about Russian attacks and corruption to attract foreign investment.