When the owner of a mobile home park in the sprawling region east of Los Angeles sought to impose a 30% rent increase two years ago, 85 residents turned to Inland Counties Legal Services for help.

Most were senior citizens on fixed incomes, paying less than $400 a month in rent, said Darrell Moore, deputy director of the legal aid organization, who worked on the case. Moore made nine trips to the park in Rialto, Calif., and attended two hearings before the city’s rent-control review board. Several residents arrived at the hearing clutching medications they said would be unaffordable if they had to pay the higher rent, he said.