Protestant recruitment to the Housing Executive is falling despite policies to improve levels, the Assembly heard.
Democratic Unionist MLA Gregory Campbell raised the issue in support of a motion demanding fairness in public sector employment, where he claimed there were many examples of Protestant under-representation.
Sinn Fein said it backed the DUP-sponsored motion because of the history of anti-Catholic discrimination and in the interests of showing fairness to all, but the SDLP's Declan O'Loan accused Mr Campbell of cherry-picking figures to support his case.
Finance minister Sammy Wilson later said figures for employment in the civil service are broadly reflective of community make-up, but he said it is acceptable to raise justifiable concerns.
Mr Campbell said: "In 2003 the Housing Executive announced that they were implementing an affirmative action plan (to) address the underlying problem of Protestant under-representation in the Housing Executive.
"You would expect to see some progress (but) the percentage of Protestants being recruited to the Housing Executive now is less than when they put the affirmative action programme in place."
He said in 2004 36.6% of those recruited were Protestant, but in 2009 the figure was 33.7%.
Mr Campbell claimed republicans and nationalists did not care about problems with Protestant recruitment in the public sector, and added: "The silence is deafening because they don't seem to mind when it is only Protestants who are being discriminated against."
The SDLP's Mr O'Loan challenged Mr Campbell's wider claims of anti-Protestant discrimination.
"Why does he single out the Housing Executive? I do not know," said Mr O'Loan.