SAN FRANCISCO — Taking one more step in a campaign against mandatory arbitration agreements, the National Labor Relations Board filed a formal complaint against San Ramon-based 24 Hour Fitness on Monday, alleging the gym company’s arbitration opt-out policy coerces employees to waive their rights to form classes and file suits against their employer.

Previously, the board had found that some mandatory arbitration clauses violate federal labor law because they deny workers the right to concerted action, or to sue together — a decision now on appeal.