PITTSBURGH — A fired district court law clerk sued a Pennsylvania county’s retirement system, saying it hasn’t set forth clear guidelines to determine how and when employees qualify for disability pensions.

Attorneys for Susan Donahue, 55, sued the Retirement System of Allegheny County, which is a private company set up under state law to administer pensions in the Pennsylvania’s second most-populous county.

The retirement system is headed by a three-member board of county officials: Controller Chelsa Wagner, Treasurer John Weinstein, and Ted Puzak, a retired county probation officer. The board is also being sued as a group.

The lawsuit accuses the board of failing or refusing “to establish clear and equally applied criteria for awarding disability retirement benefits to Allegheny County employees. … Absent such established criteria, the decision-making process is inherently irrational, arbitrary and capricious.”

Donahue’s lawsuit indicates she’s been sparring with the county and its retirement system and board since 2012, when she contends a series of previous back injuries finally became disabling.

Donahue said doctors consulted by the retirement system didn’t agree with her doctors’ findings that she was completely disabled. Donahue was deemed disabled under Social Security Administration rules in August 2014, however, and has been receiving those benefits since February 2015. Her attorneys said she’s due county benefits, too, for which she was contributed a percentage of her pay, most recently about $100 a month, since she was hired in 1982.

Timothy O’Brien, one of Donahue’s attorneys, said the retirement system’s lack of guidelines is unfair and makes the lawsuit about more than just a difference of opinion between her doctors and those consulted by the retirement board.

“The reason it’s not just a difference of opinion between doctors is because neither of those opinions can be measured against any objective standard,” O’Brien said. As a result, “Nobody knows how to prove they’re disabled.”

That’s why the lawsuit also asks that a judge deem it a class-action and, eventually, force the retirement system to develop objective guidelines for disability pension eligibility.

The retirement system’s solicitor, Brian Gabriel, said in an email Wednesday that the agency “is reviewing and will respond to the court filings in that forum. We will not have comments on the merits of Ms. Donohue’s disability application.”