Dan Donovan is pictured with Serena Stonick at the White House Christmas Ball in December 2017. They now have a young daughter together

A congressman has been accused of using his position to help his partner's son receive favourable treatment after he was arrested over heroin offences.

Dan Donovan, who represents Staten Island in New York, is said to have intervened after the son of his partner Serena Stonick's was arrested with a female friend for the 'criminal sale and possession of a controlled substance (heroin)' in December 2015.

Timothy O'Connell was detained with his friend at 112 Precinct in Staten Island, according to an allegation filed with the Office of Congressional Ethics last week.

The document claims Donovan visited the 122 Precinct and 'used his position to illegally request that officers issue O'Connell and [the friend] a "desk appearance ticket" instead of proceeding with normal arrest protocols'.

These tickets allow the arrested person to be released from custody to appear in court at a later date rather than being jailed, arraigned or sent to central booking.

Desk appearance tickets are usually issued for minor drugs offences and are rare for heroin arrests, a police source told the New York Post.

Donovan (pictured in November 2017) strongly denies allegations that he helped his partner's son receive favourable treatment after he was arrested for heroin offences

The congressman's spokesman Pat Ryan vehemently denied the congressman had used his official position to influence the judicial process 'in any way'.

'Like many families, Dan has been dealing with a loved one's opioid addiction — in private until now,' he said.

'These allegations are not only 100 per cent false, but Dan has a long history of recusing himself from matters involving close friends and family.

'Neither Dan nor anybody at his direction or suggestion or wink or nod in any way, shape or form, intervened, interfered, inserted themselves in any way into this judicial process.'

Donovan and Stonick walk through the U.S. Capitol on their way to Congress in May 2015

NYPD confirmed O'Connell and the woman, both aged 19, were arrested in the 112nd Precinct on December 3, 2015, but said no other information was available.

Ryan noted that O'Connell's arrest report showed he did not make a phone call after he was arrested.

Joe Mure, attorney for O'Connell, said his client was charged with drug possession, not sale.

All charges against O'Connell were dismissed in March 2016 and he has denied doing drugs.

He also denied getting any help from Donovan after his arrest. His female friend did not comment to the New York Post.

The person who submitted the allegation claimed it was backed up by 'multiple sources', included an active detective.

Donovan lives with Stonick and they now have a young daughter together.