The Republican National Committee has threatened a boycott of CNN and NBC in the runup to the next presidential election unless the networks cancel films they have planned on Hillary Clinton.

Reince Priebus, chair of the RNC, wrote to the heads of CNN and NBC on Monday. He warned both networks that he would seek a binding committee vote next week to "neither partner with you in 2016 primary debates nor sanction primary debates which you sponsor", unless they cancel the Clinton shows.

Last week NBC announced plans for a four-hour mini-series on Clinton, with Diane Lane in the starring role. Two days later CNN revealed it had commissioned its films division to make a big-budget documentary on Clinton to air in 2014.

"I'm writing to express my deep disappointment in your company's decision to air a miniseries promoting former Secretary Hillary Clinton ahead of her likely candidacy for the Democratic nomination for president in 2016," Priebus wrote to NBC Entertainment chairman Robert Greenblatt. The opening of his letter to CNN president Jeff Zucker substituted "miniseries" for "film" but was otherwise identical.

Priebus accused both networks of a "thinly-veiled attempt at putting a thumb on the scales of the 2016 presidential election". The programming would be unfair to others who might compete for the Democratic nomination, he said, "and to the Republican nominee, should Clinton compete in the general election".

His letter to NBC, made public on Monday, also drew attention to the fundraising efforts of employees at Comcast, NBC's parent company.

"David Cohen, Comcast's EVP, raised over $1.4m for President Obama's re-election efforts and hosted a fundraiser for the president. Comcast employees have donated $522,966 to the president and donated $161,640 to Secretary Clinton's previous campaigns," Priebus said.

The Republican Party has previously accepted donations from News Corp, which owns Fox News, without complaint.

Both letters ended with a clear threat.

"If you have not agreed to pull this programming prior to the start of the RNC's summer meeting on August 14, I will seek a binding vote of the RNC stating that the committee will neither partner with you in 2016 primary debates nor sanction primary debates which you sponsor."

NBC News said it was independent of the network's entertainment division, which is making the Clinton miniseries, and would not comment further.

CNN said: "Instead of making premature decisions about a project that is in the very early stages of development and months from completion, we would encourage the members of the Republican National Committee to reserve judgment until they know more. Should they decide not to participate in debates on CNN, we would find it curious, as limiting their debate participation seems to be the ultimate disservice to voters."

After NBC's mini-series plan was announced on 27 July Greenblatt said the show would avoid campaign laws that require equal screen time be given to presidential candidates.

"She's not going to probably declare her candidacy for two more years," NBC Entertainment chairman Robert Greenblatt said, "so this could well have aired before that."

Priebus appeared to take specific issue with those comments, saying that NBC's hope that the series would avoid equal time laws "suggests a deliberate attempt at influencing American political opinion in favor of a preferred candidate".

The RNC will hold its three-day summer meeting in Boston from 14 August. The meeting was moved to Massachusetts to show support for the city of Boston following the marathon bombing.

"It's appalling to know executives at major networks like NBC and CNN who have donated to Democrats and Hillary Clinton have taken it upon themselves to be Hillary Clinton's campaign operatives," Priebus said in a statement published on the RNC's website.

"I hope Americans will question the credibility of these networks and that NBC and CNN will reconsider their partisan actions and cancel these political ads masked as unbiased entertainment."

Both CNN and NBC hosted some of the 20 Republican primary debates held during the 2012 election. On Monday some pundits were quick to speculate that Reibus's threat may actually be a deliberate ploy to restrict the number of debates held in the 2016 cycle.

The 2012 debates were not seen as a resounding success in promoting the image of the Republican party. During one debate Texas governor Rick Perry famously forgot one of the three departments he would cut if elected president, while eventual nominee Mitt Romney was attacked as out of touch after offering a $10,000 wager in another.