State Attorney General Bob Ferguson, who successfully sued to block Trump's initial travel ban early this year, announced his latest lawsuit on Monday, three days after the new rules were issued.
Other Democratic-leaning states, including Massachusetts and California, sued on Friday, as did the American Civil Liberties Union.
Trump's policy is designed to roll back parts of former President Barack Obama's health care law, which required that most companies cover FDA-approved birth control as preventive care for women, at no additional cost. Among those FDA-approved methods is the morning-after pill, which some religious conservatives call an abortion drug even though scientists say it has no effect on pregnant women.
FILE - A one-month dosage of hormonal birth control pills is displayed Aug. 26, 2016, in Sacramento, Calif.
Victory for religious freedom?
The Trump administration touted the new policy as a victory for religious freedom, and the announcement thrilled the social conservatives who make up a key part of the president's supporters. Asked about court challenges during a briefing Friday, White House press secretary Sarah Sanders said the new rules are legal.
"The president believes that the freedom to practice one's faith is a fundamental right in this country, and I think all of us do," she said. "And that's all that today was about - our federal government should always protect that right."
But Ferguson said it violates the First Amendment, because it requires individuals to bear the burden of religions to which they don't belong, as well as the equal-protection requirements of the Fifth Amendment, because it affects women but not men.
Unfair, unlawful, unconstitutional
"President Trump's contraception rules are unfair, unlawful, and unconstitutional," Ferguson said in a news release.
The rules could affect more than 1.5 million Washington workers and dependents who receive health coverage through an employer's self-funded plan, Ferguson said. Some might have to turn to state-funded programs to receive contraceptive coverage, he said.
The vast majority of companies have no qualms about offering birth control benefits through their health plans.