Health insurers will have to start publicly justifying big rate increases, according to a new requirement of the health care law implemented Thursday to put pressure on insurance companies to hold down skyrocketing premiums. The new rules will mandate that insurers post explanations of premium increases exceeding 10 percent on their websites and submit them to state and federal regulators, who will also post them later this year. "For far too long, families and small employers have been at the mercy of insurance rate increases that often put coverage out of their reach," Secretary of Health and Human Services Kathleen Sebelius said in a statement. "Rate review will shed a bright light on the industry's behavior and drive market competition to lower costs." The new rules do not give state and federal regulators new authority to block rate hikes, however, even if government officials find the increases are unjustified. Some states already have this power, and several particularly aggressive states, such as Oregon and Rhode Island, routinely make insurers lower their rate increases after determining proposed hikes are unjustified. Even in less activist states, some regulators have been beefing up oversight of insurance companies with the help of federal grant money made available by the health care law President Barack Obama signed last year.