The Obama administration went to court Thursday to block two major health insurance mergers, siding with consumer advocates and medical groups worried that the consolidation of large national health plans could lead to higher premiums.

The long-anticipated move by the Justice Department and attorneys general in California and 10 other states,  will at least temporarily prevent Anthem Inc.’s $48-billion purchase of Cigna Corp., a combination that would create the nation’s largest health insurer.

And it will stop Aetna Inc.’s $34-billion bid to acquire Humana Inc., a merger that would have combined the nation’s third- and fifth-biggest health plans.

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After ObamaCare went into effect in 2010, Mike Merkel’s health insurance jumped from $585 per month to $1,400 per month for his family of four. When he looked into switching his insurance plan, Merkel was told by his state’s health exchange, Covered California, that he was ineligible for tax credits.