Can USCIS Require a DNA Test?

Can USCIS require a DNA test, or is this voluntary?
USCIS always has the authority to determine whether the totality of the evidence submitted is sufficient to demonstrate a relationship. By regulation, USCIS is permitted to require blood testing and so refusal to submit a blood test when requested may constitute a basis for denial of a petition. On the other hand, under existing legal authority, USCIS may only suggest that DNA testing results be submitted. For some persons, voluntary submission of DNA evidence may be the best way for some individuals to meet their burden to prove the claimed biological relationship. Otherwise, an application or petition may be denied if that burden is not met.