The Bloomberg administration is planning to require more homeless families to get jobs in order to qualify for rent subsidies, city officials said Tuesday.

For the last three years, the city had provided certain homeless families with vouchers good for one or two years of free or steeply discounted rent. Since the program began, more than 18,000 families, and some single adults, have received the so-called Advantage vouchers, more than 7,500 of them last year.

Most of those families qualified for the vouchers because they had already found work, and as a result were eligible to pay only $50 toward their rent each month for up to two years. But families who had become the subject of child welfare investigations were granted an even-more-generous voucher, good for up to two years of free rent — because of their vulnerability.

Now the Bloomberg administration is seeking to require that nearly all families have at least one member with a job before they receive a rent subsidy. Participants would also pay more toward their rent — rather than $50 a month, they would be required to pay 30 percent of their income during the first year of the subsidy. During the second year, they would pay 50 percent of the total rent.