A petition asking the culture secretary, Karen Bradley, to call in the media regulator, Ofcom, to investigate Fox’s £11.7bn takeover of Sky is on track to collect 100,000 signatures in less than two days.

On Thursday, Rupert Murdoch’s 21st Century Fox tabled a formal bid to buy the 61% of Sky it does not already own. After the announcement a petition was posted on the campaigning website 38 Degrees, titled Stop Murdoch taking over Sky, which has rapidly clocked up almost 45,000 supporters.

Lorna Greenwood, a campaigns manager at 38 Degrees, said the pace of signatories adding their support meant it would most likely pass the 100,000 mark by the end of Friday.

The petition calls on Bradley to refer the takeover to Ofcom on the grounds of potential media plurality issues. Bradley has 10 working days to decide whether the deal raises public interest issues, namely whether it potentially gives Murdoch too much influence and control over the UK news industry.

The deal would bring Sky, which owns Sky News, fully under the control of 21st Century Fox, which owns Fox News and the 20th Century Fox film studio. Murdoch also controls the Times, the Sunday Times, the Sun and the news and sport station TalkSport through the separate News Corp company.

“The fact that 37,000 people signed this petition in just 24 hours proves that there is a huge amount of public opposition to this deal,” Greenwood said. “Karen Bradley now needs to show she’s doing everything to ensure that the deal is properly scrutinised and refer it to Ofcom.”

Campaigning group Avaaz has also launched a petition calling for Ofcom to launch a “fit and proper” person investigation, given the historical issues of phone hacking, and lobbying Bradley to refer the deal to the media regulator.

It has so far drawn almost 40,000 supporters and Avaaz says that 7,000 messages have been sent directly to Bradley and the prime minister, Theresa May.

Another campaign group, Hacked Off, also launched a petition on Thursday calling for Bradley to refer the deal to regulators.

There were also 38 Degrees petitions in 2011, when Murdoch abandoned an earlier bid to take full control of Sky due to the fallout from the phone-hacking scandal. The first, which called on Ofcom to block the deal, attracted 60,000 signatures. Ofcom did not block the deal but did rule that there were media plurality issues, which resulted in Murdoch offering to spin Sky News off as a separate company. Then 38 Degrees launched a second emergency petition asking for a referral to the UK competition regulator, which drew 70,000 signatures.