US President Barack Obama is to widen background checks on buyers of firearms, in a series of measures to address gun violence.
The plans will be announced today by the president, despite opposition from Congress to new gun laws.
All sellers who operate online or at gun shows will be forced to conduct background checks on potential buyers.
Republican presidential candidate Rand Paul said he would fight the executive actions "tooth and nail".
But Mr Obama said his new measures will be within his legal authority and consistent with the Second Amendment, which grants Americans the right to bear arms.
And while they will not solve every violent crime in the US, he said they will potentially "save lives and spare families the pain" of loss.
Under the 10-point plan announced on Monday evening by the White House:
- All sellers must be licensed and conduct background checks
- FBI to increase workforce processing background checks by 50%, hiring more than 230 new examiners
- Congress will be asked to invest $500m (£339m) to address mental healthcare issues
The president's plan came after hearing recommendations from Attorney General Loretta Lynch, FBI Director James Comey and other top law enforcement officials.
He told the BBC last year his failure to pass effective gun laws was his biggest regret.