An abortion-rights group is asking a federal judge to block a Mississippi law that will ban most abortions once a fetal heartbeat can be detected, about six weeks into pregnancy.

The Center for Reproductive Rights on Thursday expanded a lawsuit it filed last year challenging a Mississippi law that banned abortions after 15 weeks’ pregnancy. A federal judge declared that law unconstitutional.

Republican Gov. Phil Bryant signed the heartbeat bill March 21, and it is set to become law July 1. It’s one of the strictest abortion laws in the nation.

Mississippi is one of several states where Republican leaders are considering abortion-restriction bills this year. Abortion opponents are emboldened by new conservatives on the Supreme Court and are seeking to challenge the court’s 1973 ruling that legalized abortion nationwide.