That means thousands of Fulton property owners should be granted the lower property valuation cited in their appeals, the lawsuit says. More than 5,000 property owners could be affected by the suit. Many of those property owners have already paid taxes based on the higher assessment, and they would be due refunds if the lawsuit is successful.

A spokesperson for Fulton County declined to comment on the lawsuit.

Sam Brannen Jr., Rachkova’s attorney, said the county could owe between $10 million and $20 million in refunds for property taxes that were improperly paid. And since property assessments that have been successfully appealed doesn’t see increases for three years, the error would multiply and cost Fulton even more in lost revenue, Brannen said.

The missed deadline would also affect cities, schools and other taxing entities that could be required to refund tax money, according to Brannen.

Brannen said the county has approved lower assessed property values when he has contacted officials about specific cases. But he said Fulton continued to work on other appeals after it was legal to do so.

“It’s a violation of equal protection,” he said. “The government is required to apply and enforce the law equally for all citizens. They just brazenly disregarded that requirement, when they knew the appeal was dead.”

Brannen said he is seeking class action status on behalf of the thousands of property owners whose appeals were started on time.

One such person is Richard Daley, an Atlanta resident who appealed the value of his Buckhead townhouse June 3, 2018. Daley, a retiree on a fixed income, said his value increased 59% in 2018, to $267,800.

Daley received a Jan. 2 letter saying the county needed more time to consider his appeal, then was informed in a Feb. 5 letter that it had been denied.

An April trip to the board of equalization reduced the value slightly, but Daley still had to pay an additional $1,445 in taxes for the home he has lived in since 1993. That’s money he said could go toward paying to install grab bars in the bathroom or widening his doors so he could stay in his home a little bit longer.

“It just drains my resources,” Daley said.

If Rachkova’s lawsuit is successful, it would mean that the $173,100 value Daley placed on his home would stand, and he would receive a refund for the additional taxes he paid.

“I have no problem paying taxes,” Daley said. “What I do have a problem with is when there’s malfeasance on the part of an agency.”

It's not the only class action lawsuit the county is involved in regarding property values. Another, which counts Atlanta City Council President Felicia Moore among its plaintiffs, claims that county appraisers matched more than 18,000 new home buyers' property values to the prices they paid for their houses, while leaving their neighbors' values alone. A former member of the board of assessors estimated last year that suit could cost $36 million in refunds.

The county has filed a motion to dismiss that suit.

Fulton also faced a suit from the state Department of Revenue, which was settled late last month. The state cried foul after Fulton county commissioners used a law from the 1880s to freeze property values in 2017 after residents complained about huge increases. As part of the settlement, the county agreed not to use the law again, and the state agreed not to force residents to pay more in taxes for that year.