While researching an answer to someone's question in this thread, I found this interesting bit of information:

On May 29, 2006, President George W. Bush signed into law the Respect for America's Fallen Heroes Act (Pub.L. 109-228), prohibiting protests within 300 feet (91 m) of the entrance of any cemetery under control of the National Cemetery Administration from 60 minutes before to 60 minutes after a funeral. Penalties for violating the act are up to $100,000 in fines and up to one year imprisonment. The bill garnered overwhelming bipartisan support in Congress with a 408–3 vote in the House, with 21 not voting, and a unanimous vote in the Senate.

On August 2, 2012, Congress passed a bill that included restrictions on demonstrators at military funerals, which became law four days later when signed by President Obama. The bill says that for 2 hours before until 2 hours after the funeral service demonstrators must stay at least 300 feet (91 m) away from the boundary of the funeral location and away from the residence of grieving family members.

And 4 states have written their own laws limiting funeral protests.

Source