DENVER - Most of Colorado's sheriffs say they are suing to block two gun-control laws scheduled to take effect this summer.

Fifty-four sheriffs, including El Paso County Sheriff Terry Maketa, are joining other gun-rights activists in trying to block a law limiting the size of ammunition magazines. The sheriffs say they're also suing to block a new law expanding background-check requirements for private gun purchases.

The sheriffs planned to file the lawsuit in federal court Friday.

Earlier this year, dozens of county sheriffs tried unsuccessfully to persuade lawmakers not to adopt the gun measures. Lawmakers raised the ammunition limit from 10 rounds to 15 rounds, but they did not reject the measure.

Gov. John Hickenlooper signed the ammunition limit and background-check bills soon after they were approved by the Legislature. They take effect July 1.