Organized labor’s early flirtation with Occupy Wall Street is starting to get serious.

Union leaders, who were initially cautious in embracing the Occupy movement, have in recent weeks showered the protesters with help — tents, air mattresses, propane heaters and tons of food. The protesters, for their part, have joined in union marches and picket lines across the nation. About 100 protesters from Occupy Wall Street are expected to join a Teamsters picket line at the Sotheby’s auction house in Manhattan on Wednesday night to back the union in a bitter contract fight.

Labor unions, marveling at how the protesters have fired up the public on traditional labor issues like income inequality, are also starting to embrace some of the bold tactics and social media skills of the Occupy movement.

Last Wednesday, a union transit worker and a retired Teamster were arrested for civil disobedience inside Sotheby’s after sneaking through the entrance to harangue those attending an auction — echoing the lunchtime ruckus that Occupy Wall Street protesters caused weeks earlier at two well-known Manhattan restaurants owned by Danny Meyer, a Sotheby’s board member.

Organized labor’s public relations staff is also using Twitter, Tumblr and other social media much more aggressively after seeing how the Occupy protesters have used those services to mobilize support by immediately transmitting photos and videos of marches, tear-gassing and arrests. The Teamsters, for example, have beefed up their daily blog and posted many more photos of their battles with BMW, US Foods and Sotheby’s on Facebook and Twitter.