I believe it is in reference to the US government's (or possibly some states') policies concerning abortions.
For most of its existence, it basically said that no foreign NGO could receive US funding for family planning if that NGO performed or promoted abortion for family planning.
President Trump has expanded it to say that no foreign NGO can receive any US global health assistance if it performs or promotes abortions.
Providing accurate medical information about abortion is interpreted by some as falling under the Mexico City policy.