WASHINGTON — In the early 2000s, after Michael Froman decamped from the Clinton Treasury Department for Wall Street, he called his old law school colleague Lori Wallach, now an anti-globalization activist, with an unusual proposal.

Would she fly to Citigroup’s training center in Westchester County, N.Y., to explain to company executives from around the world that liberal activists who had derailed a World Trade Organization expansion were not all fuzzy-headed anarchists and should be taken seriously?

“Really?” she recalled shouting incredulously to the assistant who took the call, before making an offer she figured he would have to refuse. “Tell them my speaking fee is $20,000, and I need a private plane right to Westchester.”

Demands met, her assistant shouted back, “We should’ve asked for $50,000.”

Ms. Wallach, the longtime leader of Public Citizen’s Global Trade Watch and a skeptic on what she calls “job killing” trade agreements, and Mr. Froman, the United States trade representative trying to land the largest trade accord in a generation, have occupied different worlds and economic stratospheres since their days at Harvard Law School.