WASHINGTON — A California congresswoman held a closed-door briefing on pyramid schemes for fellow lawmakers on Wednesday.

The information session hosted by Rep. Linda Sanchez (D-Calif.), the first member of Congress to ask the Federal Trade Commission to investigate Herbalife over pyramid concerns, comes less than a week after Sen. Edward Markey (D-Mass.) called on the regulator to investigate the LA company.

Sen. Markey “certainly bumped up the profile” of the call for an Herbalife probe, Sanchez told The Post before the event. “Hopefully the FTC will take this seriously.”

Roughly 25 people attended the session at the Cannon House Office Building — mostly lawmakers’ staffers — and half said at the beginning they couldn’t describe what amount to a pyramid scheme.

The audience also included the FTC’s expert on the illegal practice, Peter Vander Nat.

“We need to keep the pressure on these federal agencies and the state attorneys general,” said Sally Greenberg, executive director of the National Consumers League, which was the first organization to ask the FTC to investigate Herbalife.

Greenberg told the group that she and Brent Wilkes, the executive director of the League of Latin American Citizens, had met with the FTC regarding an Herbalife investigation “and we are hoping to have another.”

Wilkes, who also spoke at the briefing, said “predatory practices of pyramid schemes are a significant cause of the wealth gap” in the US.

The focus by pyramid schemes on undocumented immigrants is particularly troublesome because they are the least likely to complain, he said.