May 7, 2014 -- The landlord of a San Francisco rent-controlled apartment building who told tenants they must have an annual income of at least $100,000 and a FICO credit score of at least 725 has written another memo. This time, he says it was all a mistake.

An anonymous tipster told local blog Hoodline that landlord Robert Shelton distributed a new note on Tuesday rescinding his previous letter of the income and credit score requirement.

“After reflection and guidance, I hereby rescind the April 25, 2014 correspondence to you,” Shelton wrote. “The information contained was flawed.”

San Francisco Landlord Tells Tenants: Make $100K, Have 725 Credit Score

Some landlords want old tenants out so that they charge new ones higher rent, explains Delene Wolf, executive director of the San Francisco Rent Board. She told ABC News she has specialized in local rent control issues for 30 years. But, she said, “I have never seen rents like this -- not even during the dotcom boom. A teeny one-bedroom can go for $4,000 a month.”

The bidding-up of rents has caused a frenzy, she said, noting the market "is amazing -- but not in a good way.”

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Ted Gullicksen, director of the San Francisco Tenants’ Union, told ABC News the residential vacancy rate in the city is only about 2 percent now.

“Anything under 4 percent is considered a crisis." When an apartment opens up, it’s not uncommon for 50 to 75 people to show up for the open house, he said, and those aspiring renters bid against one another. The driving engine of the bidding, he said, are the high salaries paid to tech industry workers.

The only way for landlords to get a market rate is for them to offer either a brand new apartment or one newly vacated. There are, Wolf said, 16 legal ways for a landlord to get a tenant out, but re-screening for income is not one of them.

Once a tenant has moved in, Gullicksen said, it's illegal for the landlord to impose a minimum income or otherwise attempt to re-qualify him or her.

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When ABC News reached Shelton by phone, he hung up. When an ABC News reporter knocked on his door, Shelton closed it without responding.