The pressure on New York City mayoral contender Bill Thompson to end his candidacy to avoid a divisive Democratic runoff is mounting as former supporters of NYC Council Speaker Christine Quinn announce their support for the frontrunner, NYC Public Advocate Bill de Blasio.

It’s not even noon yet, and three press releases announcing endorsements of de Blasio have already landed in my in-box. All three came from organizations or individuals that had backed Quinn in her failed attempt to succeed Mayor Bloomberg in City Hall. They are:

– Planned Parenthood of NYC’s Political Committee Board, which touted de Blasio’s “long history” of “legislating and advocating on behalf of reproductive health and justice.”

– United Auto Workers (UAW) Region 9A, a founding member of the labor-backed Working Families Party (which remained neutral in the Democratic mayoral primary):

“The Democratic field for Mayor this year was comprised of candidates who are passionate about improving the quality of life for workers, the middle class, and New York’s most vulnerable, such as the poor and senior citizens,” said UAW Region 9A Director Julie Kushner.

“We are confident that Bill de Blasio will be a mayor for all New Yorkers, raising the standard of living for those who have seen it stagnate or erode…New York is a leader in the arts, education, diversity, and innovation, yet it can be an unforgiving place to live at times. It can take its toll on those who make it the vibrant city it is. With Bill de Blasio as mayor, our city will soften its hard edges and allow all to flourish and thrive, not just some.”

– Assemblywoman Deborah Glick, the first openly gay member of the state Legislature:

“New York, now more than ever, needs a Democratic Mayor to address the corrosive impact of the increasing income inequality in our city. We must move forward united and committed to ensure that all New Yorkers benefit from the cultural, educational and economic vibrancy that is the envy of the world.”

“…I ask all Democrats to come together now that the primary election is behind us. We have an urgent need to elect a Democratic Mayor and that Mayor should be Bill de Blasio.”

None of these statements overtly calls on Thompson to end his campaign, which he has so far refused to do until all the paper ballots are counted – a process that won’t even begin until next week. But all this talk of “unity” send a pretty clear message that the time for intra-party fighting is over, and the party must unite behind one candidate or risk its shot at regaining control of City Hall from the GOP for the first time in 20 years.

Yesterday, a number of Democratic power brokers started to call for Thompson to throw in the towel, including his friend and ally, the Rev. Al Sharpton, who was reportedly disappointed by the fact that de Blasio, who is white, though married to a black woman and the father of two inter-racial children, fared better among black voters than Thompson, who is himself black.

Thompson’s own campaign chairwoman, Regents Chancellor Merryl Tisch, called de Blasio the “clear winner” of the primary, and said she doesn’t believe there’s much “appetite” for a runoff in the Democratic Party, but she stopped short of calling on Thompson to drop out. Also, the influential Hotel Trades Council, which had backed Quinn in the primary, announced it was switching its alliance to de Blasio.