Children born abroad to certain United States service members and other federal employees will no longer be granted automatic citizenship under a Trump administration policy set to take effect in October.

Parents of those children, including those born on military bases, will have to apply for citizenship on the children’s behalf before they turn 18, according to a United States Citizenship and Immigration Services policy released on Wednesday.

The policy appeared to be aimed at military families who have not lived in the United States for years. According to the immigration agency, the change would not affect the children of families with at least one parent who is an American citizen and has lived in the United States for at least five years.

It was unclear how many families the change would affect.

A spokeswoman for the Pentagon said the impact would be small, without specifying how many parents would be required to apply for citizenship for their children under the change. A spokeswoman for the citizenship and immigration agency, which oversees legal immigration, also declined to provide the number of families who would be affected.