A San Francisco credit union is suing the city's transportation agency for $28 million or more in compensatory damages over a failed taxi medallion program.

The $1 billion San Francisco Federal Credit Union filed a civil lawsuit Tuesday in a California Circuit Court claiming the San Francisco Municipal Transportation Agency allegedly violated certain contract provisions of a public-private partnership program to protect the credit union from suffering millions of dollars in damages.

San Francisco FCU President/CEO Jonathan Oliver said filing the lawsuit was a difficult decision considering that the credit union was founded in 1954 by a group of city employees. Over the years, the credit union has partnered with San Francisco to help members afford homes in one of the most expensive cities in the country and it has supported many financial programs and community events.