“It’s unacceptable to me,” he added. “Within the bounds of the law, I want to find out what our recourse is.”

Recourse has so far taken the form of Appraisal Systems representatives’ setting up shop at folding tables in a basement room at City Hall to meet with worried property owners. On Tuesday, a stream of frightened and fuming residents, including Jose Breda, trudged in and out.

“They are robbing the people,” said Mr. Breda, 58, a landlord whose six-unit apartment building’s assessment more than doubled from its valuation in 2003, the last time properties were assessed in Newark. “This is ridiculous; they make numbers out of space.”

The city will not announce its new tax rates until the summer, but many like Mr. Breda say they fear that rates will not drop in proportion to the amount their properties were judged to have appreciated.

Some of the revaluations may be wrong because property owners did not provide enough information, said Rick DelGuercio, president of Appraisal Systems. In 2011 and 2012, the company sent certified letters to about 7,500 owners asking for information on rents, expenses and utility costs. Only about half of the questionnaires were returned, Mr. DelGuercio said, so appraisers made many estimates. In other places, including Hackensack, Fair Lawn and Gloucester County, the survey return rate was between 75 percent and 80 percent, he said.

“We were doing the best we could with the lack of information; 50 percent is low,” Mr. DelGuercio said, adding that company representatives stationed in City Hall through the end of the month can help fix errors.

After the real estate market crashed in 2008, commercial properties lost less value than residential properties did, Mr. DelGuercio said. He estimated that about 10 percent more of Newark’s tax revenue would have to come from commercial properties than residential.