A subsidiary of HSBC has been accused in an American lawsuit of charging higher mortgage rates to black people than to their white counterparts.

Lawyers for Suyapa Allen are seeking the right to bring a class action against the bank for allegedly discriminating against black borrowers by offering more expensive home loans.

Ms Allen’s lawsuit – brought in a court in Boston - claims that HSBC and Decision One, its American mortgage unit, have used a discretionary pricing policy that has a discriminatory impact on black borrowers.

In America, lenders are required by law to be fair in their lending practices under two pieces of legislation, the Equal Credit Opportunities Act and the Fair Housing Act.

HSBC Finance was formed after the global banking group bought Household International in 2003. The wholly owned subsidiary offers sub-prime loans to people who typically have poor credit histories and low incomes. HSBC Finance sells mortgages through a network of independent brokers in America within a business called Decision One. Decision One allows the brokers to fix part of the price of the sub-prime loan.

According to the lawsuit, the discretionary element in the pricing of such mortgages gives brokers the chance to charge black people more than white people. “HSBC’s pricing policy accounts for a significant portion of the disparity,” the lawsuit said. “[It] is unrelated to a borrower’s objective credit characteristics, such as credit history, credit score . . . and results in purely subjective charges that affect the rate otherwise available to borrowers.” HSBC Finance is facing another class action for alleged discriminatory lending. In July, the National Association for the Advancement of Colored People filed a class action against a dozen mortgage lenders, including HSBC Finance and Washington Mutual, alleging that black people received higher-interest sub-prime loans than white people.

Discriminatory lending is a sensitive issue in the United States. In 2004, banking regulators demanded that lenders compile data on how much they lent and to whom so they could track lending trends.

Last week, the regulators, which include the US Federal Reserve, published their data for 2006. It showed that black and Hispanic borrowers were charged higher interest rates on their mortgages more often than their white counterparts and were turned down more often for home loans.

However, the data does not necessarily prove that lenders are discriminating on the grounds of race. Banking regulators are now sifting through the data to ascertain whether other factors influenced the level of interest rate charged, such as poor credit histories of the borrower.

“The case is about HSBC’s practice of opening different doors in different communities,” Gary Klein, a lawyer for Ms Allen, said.

HSBC Finance said: “We take our fair lending and consumer protection practices very seriously. Accordingly, we have conducted and continue to conduct reviews of our lending programs, and we are confident that we are treating our customers fairly and with integrity.”

HSBC did not discriminate against Peter Lewis because of his sexual orientation, an employment tribunal in Stratford, East London, ruled yesterday. The former head of equity trading sued the bank last year for £5 million, accusing it of firing him because he was gay. He lost 12 of his 16 claims, but the Employment Appeal Tribunal ordered a fresh hearing into four of them. An HSBC spokesman said that the bank had always maintained that Mr Lewis’s claims were groundless.