Now 39, she is one of several coaches to assume a leadership role, but the other members say Ms. Chiang’s steady, dispassionate involvement solidified their resolve. Many of them said they worried that their pro-union activity could jeopardize their ability to work at Sky Rink in the future.

“Angela is our Norma Rae,” Amy Engeler, a coach at Sky Rink for 28 years, said, referring to the character played by Sally Field in the 1979 film based on the organizing efforts of Crystal Lee Sutton. “But she’s no firebrand. She’s very quiet and thoughtful, so when she was willing to take a stand, it made us all take a look.”

The collective intensified its organizing efforts last summer, after the company presented the coaches with a new contract that the coaches said cost them money. They said that after they raised objections, the company demanded that each coach sign the new contract by noon on Sept. 4 — Labor Day. The coaches felt compelled to sign, but they each added a line after the signature: “Member, NYC Coaches Collective.” It was a symbolic gesture, to be sure, but Ms. Chiang said it felt empowering. Six months later, Ms. Chiang received the email informing her that she was no longer a Sky Rink employee.

Ms. Halasa was told about her dismissal not long after she handed out Coaches Collective fliers at a gala dinner at Chelsea Piers. The dinner was hosted by North Star Fund, a social justice organization. Security guards tried to stop Ms. Halasa, but Jennifer Ching, the fund’s executive director, who had granted her permission to distribute the cards, intervened. Chelsea Piers employees later told Ms. Halasa that they were concerned that the fliers were related to war protests.

Nine days later, she was fired. The reason given, she said, related to a letter she had written on behalf of a student’s mother, who was going through a divorce. The letter angered the student’s father, who complained to Sky Rink. Ms. Halasa said that management discussed the letter with her in February and told her at the time it was not actionable. She, too, believes she was fired for her role in the union.