The Fox television network looks set to broadcast the NRA-sponsored Nascar Sprint Cup on Saturday, despite a plea from a Connecticut senator to pull the broadcast due to the pro-gun association's "extreme" agenda.

Chris Murphy, a Democrat, wrote a letter to Rupert Murdoch, the chief of Fox's parent company, News Corp, saying that the high-profile car race was taking place against the backdrop of a fierce national debate over possible gun control legislation. Those laws, being mulled by the Senate, have been brought in due to the Newtown shooting, in which 20 children and six adults were killed at a school in Connecticut at the end of last year.

In his letter, Murphy said the powerful NRA gun lobby – which since Newtown has been arguing for the placement of armed security guards in schools – had an "extreme nature".

"I urge you to not broadcast this race on April 13th. Inserting Fox Sports in this debate at this critical time will give credence to an extreme organization that is opposed to reasonable policies to stem gun violence," Murphy wrote.

Another issue is the tradition at the race, which is being held in Texas, of giving a rifle and six-shooters for the winning drivers to shoot – though the weapons fire blanks. "This celebration of guns is inappropriate in the immediate wake of the Newtown massacre," Murphy wrote.

The letter follows a missive that Murphy sent a month ago to Nascar boss Brian France, asking him to reconsider the NRA sponsorship. However, there appears little chance that the race will not be shown live. It is expected to see around 150,000 people watching in person in Texas and an audience of millions on television.

A representative of the families at Newtown did not immediately respond to a request for comment.

Nascar organisers have said they intend to take a "closer look" at the sport's sponsorship process, although they indicated that the NRA deal does conform to Nascar's existing criteria.

Murdoch, however, has shown himself to be in favour of gun law reforms in the wake of Newtown. On his Twitter page, Murdoch once asked: "When will politicians find courage to ban automatic weapons?" He has also urged president Barack Obama to act. "Nice words from [Obama] on shooting tragedy, but how about some bold leadership action?" he stated.

Obama is trying to do exactly that, waging a high-profile campaign to pass gun control. On Saturday, a mother of one of the Newtown victims used the president's weekly address to issue a heartfelt plea for tighter gun controls. Francine Wheeler, whose six-year-old son Ben died at Sandy Hook elementary school, urged Americans to press Congress to pass "commonsense" laws including universal background checks on would-be weapons buyers