Alec Baldwin says a five-year firearm sentencing enhancement in the charges against him is unconstitutionally based on a law passed after the shooting on the set of the film Rust and has asked a judge in New Mexico to dismiss it.

“The prosecutors committed a basic legal error by charging Mr Baldwin under a version of the firearm-enhancement statute that did not exist on the date of the accident,” a court filing from Baldwin’s lawyers said.

Baldwin and Hannah Gutierrez-Reed, the weapons supervisor on the set of the western, were charged last month with felony involuntary manslaughter in the shooting death of cinematographer Halyna Hutchins.

Hutchins died shortly after being wounded during rehearsals at a ranch on the outskirts of Santa Fe on October 21, 2021.

Baldwin was pointing a pistol at Hutchins when the gun went off, killing her and wounding director Joel Souza.

Hutchins’ parents and sister filed a lawsuit over the shooting on Thursday, after a similar suit filed by her husband and son was settled.

Baldwin’s lawyers also filed a motion on Tuesday to disqualify the special prosecutor in the case, asserting that her position as a state lawmaker constitutionally prohibits her from holding any authority in a judicial capacity.

Baldwin’s legal team is aggressively pushing back before he has even made his initial court appearance, which is scheduled to take place by videoconference later this month.

Alternate legal perspectives

The manslaughter charges against Baldwin and Gutierrez-Reed include two alternative standards and sets of penalties and a jury can decide which to pursue, according to prosecutors.

One version would require proof of negligence, which is punishable by up to 18 months in jail and a $US5000 ($A7,238) fine under New Mexico law.

The second alternative is reckless disregard of safety “without due caution and circumspection”.

It carries a higher threshold of wrongdoing and includes the gun enhancement that could result in a mandatory five years in prison.

But legal experts said Baldwin has a strong chance of seeing it thrown out.

“This is a violation of the ex post facto clause of the constitution,” said Neama Rahmani, president of West Coast Trial Lawyers.

“The government can’t pass a law and retroactively punish someone under that law. The judge is likely going to toss that enhancement and so Baldwin is just looking at a maximum sentence of 18 months in jail.”

A message seeking comment from prosecutors on the motion was not immediately returned.

-AAP