The flight attendants, represented by the Association of Flight Attendants-Communications Workers of America, are highlighting the fact that their contract becomes amendable today.
Union spokeswoman Sara Nelson said the employees have made a number of concessions over the past seven years. Beginning today, she said, those cuts should end.
Nelson was participating in a picket line this morning at Chicago's O'Hare International Airport.
She said that after the airline went bankrupt several years ago, the union accepted cuts of more than $3 billion in pay, working conditions and health care, along with the termination of workers' pensions.
"We were promised the cuts would remain in place for a certain amount of time, but we continue to live under these concessions while executives have rewarded themselves with millions of dollars in bonuses," she said.
Union officials say a full contract proposal has yet to be proposed. Negotiations began in April, they said.
Nelson said the flight attendants "are going to keep protesting until we get a contract."
Besides San Francisco and Chicago, flight attendants are also protesting in Los Angeles, Las Vegas, Seattle, New York, Washington D.C., Boston, Atlanta, Denver, Frankfurt, Hong Kong, London, and Tokyo.
The protest at San Francisco International Airport was scheduled to take place from 10 a.m. to noon at the United departure level of Terminal 3.