6 CFR §19.10

1. (a)If a State, local, or Tribal government voluntarily contributes its own funds to supplement Federally supported activities, the State, local, or Tribal government has the option to segregate the Federal assistance or commingle it.
2. (b)If the State, local, or Tribal government chooses to commingle its own and Federal funds, the requirements of this part apply to all of the commingled funds.
3. (c)If a State, local, or Tribal government is required to contribute matching funds to supplement a Federally supported activity, the matching funds are considered commingled with the Federal assistance and therefore subject to the requirements of this part.