I need to find the status of the individual units and what the current legal rents are.

I don't think there's anything wrong with going to the legal rent."

Merely determining what the correct legal rent roll should be has been a problem in the takeover process.

Vacant regulated apartments are deregulated when the legal rent is $2,000 or more a month.

The cost to the city, which rises each year as legal rent ceilings rise, reached $91 million last year.

Even then, he said, the tenant can charge a roommate no more than his or her proportionate share of the legal rent.

In many cases a normal vacancy allowance and rent-guidelines increase will be enough to put the legal rent at $2,000.

Landowners were able to raise the legal rents on their lands; sometimes as much as ten-thousandfold.

If the legal rent charged the prime tenant goes up during the term of the sublease, the increase may be passed on to the subtenant.

"In such a case, the new owner is not only ignorant of what legal rent should be, but he is also incapable of finding out."

Judges may demand now to know the legal rent, but a certification requirement would undoubtedly slow all dispossess actions further.

Do I have to sign a lease before I have a right to demand proof on the legal rent?

Under rent-stabilization rules, a landlord can begin charging open-market prices when the legal rent after a vacancy reaches $2,000 a month.

Under the rent stabilization law, she said, a subtenant may be charged 10 percent above the legal rent for a furnished apartment.

Six years ago, state lawmakers adopted amendments that let landlords deregulate vacant units if they get the legal rent up to $2,000 a month.

Under state law, landlords are prohibited from soliciting payments for rent-regulated apartments above the legal rent ceilings.

Having that list, Mr. Ng said, will provide the tenant with a point of reference from which he or she can determine the legal rent.

Because it puts rent-control restrictions on co-op owners, even if their maintenance and mortgage costs exceed the legal rents they can charge.

That gets the new legal rent to $2,084, and deregulates the apartment so that its owner can charge whatever rent the market will bear.

Most recently vacancy decontrol was applied to apartments in which the first legal rent after a regulated tenant departed was $2,000 a month or more.

He added that while tenant advocates might argue otherwise, applying the four-year limitation to the calculation of the last legal rent was within the agency's power.

"The code only provides that the legal rent must be shared proportionally among all occupants," Ms. McGuire said.

In addition, apartments can be removed from regulation when the legal rent reaches $2,000 and the current tenant's income exceeds $175,000 a year for two consecutive years.

It is illegal for New York City landlords to solicit payments for such apartments above the legal rent ceiling.

Once the legal rent is known, the letter writer can immediately reduce the rent payment to that amount and then decide on what other option to pursue.