Five midsized nonprime lenders have been accused of redlining by a major advocacy group, which has accused them of using loan size and collateral limits to deny credit to minorities. In complaints filed with the Department of Housing and Urban Development, the National Community Reinvestment Coalition said that Nova-Star Financial, Fieldstone Investment, Corp. SouthStar Funding, EquiFirst Corp. and Gelt Financial Corp. have violated the federal Fair Housing Act because their policies of not funding…