The Portland City Council on Monday was debating a proposal to increase the number of affordable housing units required in larger development proposals.

Under Mayor Michael Brennan in 2015, the council adopted an inclusionary zoning ordinance that required at least 10 percent of the dwelling units in developments with 10 units or more be made affordable to middle-income earners. That income bracket is defined as up to 120 percent of area median income, which currently ranges from $68,950 for a single person to $98,500 for a family of four.

Developers can avoid the requirement by paying the city $100,000 for every affordable unit not built. That money goes into the city’s housing trust fund, which is used to help build affordable housing.

As of May, the city ordinance has applied to 18 projects, totaling 693 units, of which 187 are workforce units. Several projects have decided to use the buyout provision. If all of those projects move forward, the city could receive $1.3 million from developers.

Last year, Mayor Ethan Strimling asked the council to double the amount of affordable units required by the ordinance. He argued the change would help address the continuing shortage of affordable rental housing in Portland. He also wanted to lower the maximum annual income for a family of four purchasing or renting workforce units.

City staff recommended two additional changes. One was to remove a 6-year sunset clause from the original ordinance. The second was to eliminate the ability for developers to round down in their calculations on affordable units and instead pay a fractional fee.

At Monday’s meeting, Councilor Brian Batson proposed increasing the requirement from 10 percent to 18 percent. The council had not yet voted as of press time.

A majority of the 10 people who spoke were housing developers who opposed the ordinance.

Critics argued beefing up the ordinance would stifle residential construction in the city. They also worried it was too soon to make changes to a rule that is not yet three years old.

“Please remember that 18 percent of zero is still zero,” developer Jonathan Culley of Redfern Properties said.

Supporters wanted the ordinance to go further. They suggested removing the option for developers to pay a fee in lieu of building affordable units or increasing that fee above its current level.

“Portland is in a very real crisis of affordable housing,” said Carolyn Silvius, an advocate with Homeless Voices for Justice.