Not content with just driving Gerald and Elaine Schuster out of the national Democrats' big-buck fund-raiser in Boston, the state's labor leaders are vowing to drive the wealthy Newton couple out of the party altogether. The Massachusetts AFL-CIO and the union representing the workers at Gerald Schuster's nursing home are not backing down from their threat to throw picket lines up around the event. Their condition for calling off the pickets: the party's pledge not to take any more money from the Newton couple. The hard line caught party leaders off guard, particularly after Elaine Schuster last week backed out of the Boston event - which features former president Bill Clinton - to allow it to go foward. The Schusters have raised millions of dollars for Democrats. No one quite knows what is going to happen now. National chairman Terence McAuliffe is reportedly livid at the state party for siding with the unions against the Schusters. US Senator [John F. Kerry], a featured guest and friend of the Schusters, says he won't cross a picket line. Clinton too is not the kind of Democrat to cross union lines. "I am hoping at the end of the day, everyone will do the right thing," said Alan Solomont, a major Democratic Party fund-raiser and Schuster friend.