In a critical step in a longstanding fight, Texas formally said on Tuesday that it was ending Medicaid funding of Planned Parenthood, a move the group said could affect 11,000 patients.

The office of inspector general for the Texas Health and Human Services Commission issued a final notice terminating Planned Parenthood’s enrollment in the state-funded health care system for the poor. If it is not stopped, the termination will be effective in 30 days.

Planned Parenthood officials said on Tuesday night that they would continue to provide birth control, cancer screenings, H.I.V. tests and other care to Medicaid patients and seek an injunction in federal court to stop the state. The group sued the state in 2015 after a preliminary notice was filed, but the court case has lingered pending further action by the state.

At stake is about $4 million a year in Medicaid funding. The formal notice is the latest salvo in a legal and political fight that dates back years but intensified 15 months ago when the state issued a preliminary notice to end Medicaid funding for the group’s 34 health care centers.