Activists will launch a last-ditch effort to prevent Donald Trump’s tax bill from passing in the Senate on Monday, with scores of groups planning to lay siege to politicians’ offices.

Indivisible, the progressive group that aims to use Tea Party tactics to thwart the Republicans, has called for a day of action to stop the tax legislation, which the Senate is expected to vote on in the week after Thanksgiving.

According to some estimates, the GOP bill would actually raise taxes on middle-class workers over the next decade, and leave 13 million more people without insurance. A different tax bill passed the House on 16 November.

“Republicans are trying to rush this tax bill through,“ said Angel Padilla, the policy director at Indivisible. “And this is kind of standard practice for Republicans now – trying to rush things without any real public input. That’s what we saw on the healthcare bill and that’s what’s happening now.”

Activists are planning to hold sit-ins and demonstrations outside Republican senators’ offices across the country, in a protest they have dubbed “#TrumpTaxScam Sit-Ins”.

Indivisible, which is made up of more than 6,000 groups nationwide, has called for people to target seven senators in particular who it believes could vote against the bill: John McCain, Jeff Flake, Lisa Murkowsi, Susan Collins, Rob Portman, Shelley Moore Capito and Bob Corker.

“They’re the most important of the bunch,” said a post on the Indivisible website.

In Phoenix, people are planning a “revolving sit-in” at the offices of Arizona senators McCain and Flake. Both are wavering on the legislation – Flake has said he is concerned it will add to the national deficit while McCain has previously voted against tax cuts that disproportionately favor the wealthy. The reductions in the Senate bill would most benefit the country’s highest earners.

Tanya Luken, an organizer with Indivisible Phoenix, said small groups of activists will sit outside the senators’ offices for 30 minutes at a time before being subbed out for others to reduce the risk of arrest.

“If you’re going to reform income tax law that is not the way to do it. I’m all for simplifying things but this tax bill does nothing but redistribute wealth upwards,” Luken said.

In Alaska an Indivisible group is planning a sit-in at Murkowski’s office in Anchorage. Murkowski rebelled against her party to vote against Republicans’ healthcare reform in July, although on Tuesday she wrote an op-ed in the Fairbanks Daily News-Miner which suggested she might vote for the tax bill.

“I believe that the federal government should not force anyone to buy something they do not wish to buy in order to avoid being taxed,” Murkowski wrote – a reference to the Affordable Care Act’s “individual mandate”, which will be removed under the Senate tax plan, destabilizing healthcare insurance and, according to the Congressional Budget Office, seeing an additional 13 million people lose insurance. The CBO also predicted the tax bill would add $1.5tn to the nation’s debts.

In addition to Monday’s protests, a group called Not One Penny is stepping up the pressure on Republican senators by running TV adverts in key districts, highlighting inequality in the tax legislation. Both the Senate and the House are on recess this week, and politicians are likely to be spending time in their home states.

The group ran an advert in Maine on Tuesday which urged Republican senator Collins not to “lose her way”. Collins, like Murkowski, voted against the GOP’s healthcare legislation in the summer and activists hope she will do likewise on the tax bill.

Activists with the progressive group March forth Maine are planning to hold a demonstration outside Collins’ office in Portland, Maine, on Monday.