Earlier this year, Portland's police and fire retirement fund settled a case in which it overpaid nearly more than 900 pensioners.

Now, the fund faces a massive suit claiming that it's also underpaying retirees.

Two former Portland Fire Bureau employees filed a class-action lawsuit in Multnomah Circuit Court yesterday, claiming the city's Fire and Police Disability and Retirement Fund has owed nearly 300 pensioners a pay bump for years, but hasn't paid up.

It's unclear how much money's at issue in the case, but, if successful, the plaintiffs would receive a three percent pay bump retroactive to 2008.

"It's gonna add up," says Greg Hartman, who represents plaintiffs Clark Stephens and Robert Wuerth. "The firefighters are entitled to be paid."

The dispute stretches back to 2009, when a dozen retirees first filed suit against the pension fund. Two things you need to know to understand their claims:

•The pensioners, who all retired prior to 1990, are beneficiaries of a now-defunct benefit plan that dictates they're paid 60 percent of the highest firefighter salary.

•Whereas many fire bureaus require only certain employees to be licensed to drive fire trucks and other vehicles, the Portland Fire Bureau mandates all firefighters become certified "apparatus operators."

So in 2007, when the city signed a contract giving those operators a pay bump, retirees argued their benefits should get the same. Nope, the city said, the raise was a "specialty payment" and so not eligible.

The pensioners sued in 2009, but a judge ruled they hadn't exhausted all their options. They appealed, Hartman said, and that appeal is still pending. In the meantime, the retirees made their case to the state's Office of Administrative Hearings. In 2011, an administrative law judge agreed that the fund should pay up.

But city officials appealed that decision, Hartman said, meaning the dispute now has two cases before the court of appeals.

"There are actually several cases and they all fundamentally focus on the same thing," said Hartman, whose firm also represented retirees seeking to keep years of mistaken overpayments by the pension fund. In a deal reached earlier this year, that group got to keep roughly 40 percent of the unearned money.

Neither fund Director Sam Hutchison nor Interim City Attorney Harry Auerbach have returned calls for comment.