The Justice Department has filed an antitrust lawsuit against real estate software company RealPage, accusing it of an illegal system that allows landlords to coordinate on rent increases.

The lawsuit accuses the company of violating antitrust laws with its algorithm that landlords use to determine recommended rental prices for apartments. Justice Department officials say the algorithm allows landlords to match their prices and avoid competition that would keep rents low.

“Americans should not have to pay more rent just because a corporation found a new way to conspire with landlords and break the law,” Attorney General Merrick Garland told reporters.

In a statement, RealPage said the Justice Department’s demands were “baseless and would do nothing to make housing more affordable.”

Mortgage rates fall to 15-month low

The average interest rate on 30-year mortgages fell this week to its lowest level in 15 months, a welcome relief for homebuyers navigating a housing market that remains unaffordable for many Americans.

The interest rate fell from 6.49 percent last week to 6.46 percent, said mortgage buyer Freddie Mac. A year ago, the average interest rate was 7.23 percent.

The average interest rate is now at its lowest level since mid-May last year, when it was 6.39%.

Borrowing costs for 15-year fixed-rate mortgages also fell this week — good news for homeowners looking to refinance their mortgage at a lower rate. The average interest rate fell to 5.62% from 5.66% the previous week. A year ago, it averaged 6.55%, according to Freddie Mac.

“Although mortgage rates have remained relatively stable in recent weeks, weaker economic data suggests that rates will trend slightly lower through the end of the year,” said Sam Khater, chief economist at Freddie Mac.