Starbucks will use its coffee cups to encourage US politicians to strike a deal and prevent the American economy from going over the so-called 'fiscal cliff' in the New Year.
Its chief executive Howard Schultz is urging workers in around 120 Starbucks shops in the American capital Washington to write "come together" on customers' cups today and tomorrow.
The campaign aims to send a message to Senate politicians as government negotiations continue to avoid tax increases and huge spending cuts.
Boris Johnson has condemned "sneering" at Starbucks after the firm volunteered to pay millions of pounds more tax.
The London Mayor defended companies like the coffee chain who had been minimising their bills to the Exchequer, insisting they had a duty to shareholders.
Speaking on Sky News's Murnaghan programme, Mr Johnson admitted that Starbucks had got into a "hell of a mess".
But he said:
Imagine that you are the corporate finance director of one of these companies.
Your job is to look at the law as it stands. Your fiduciary duty to your shareholders is to minimise your tax exposure.
It is not to say, 'this looks pretty bad, we had better write a huge cheque to the Government ex-gratia and show that we are good citizens'.
Companies do not work like that.
Now that Starbucks has stepped up to the plate and announced they are going to be making this payment I think rather than everybody sneering at them people should welcome that.
My point is it is a bit unfair to bash the companies and then sneer at them when they try to do good.
Coffee chain Starbucks has been hit by protests at branches across the country over its tax arrangements, despite announcing changes to its payments.
One store in Vigo Street, central London, was occupied by protesters at 12pm and then temporarily closed.
Dozens of activists chanted "pay your tax" and waved placards and banners outside, shutting off the street to traffic under the gaze of the police.
Coffee chain Starbucks is braced for protests over its tax arrangements despite announcing changes to its payments.
The US-owned giant said it expects to pay around £10 million in UK corporation tax for each of the next two years, following the revelation that it paid just £8.6 million in 14 years of trading in Britain and nothing in the last three years.
Activist group UK Uncut said it was planning more than 40 demonstrations across the country, "transforming" Starbucks stores into refuges, creches and homeless shelters.
It is an outrage that the government continues to choose to let multinationals like Starbucks dodge millions in tax while cutting vital services like refuges, creches and rape crisis centres. It does not have to be this way. The government could easily bring in billions by clamping down on tax avoidance that could fund vital services by clamping down on tax dodging.
A spokesman for JPMorgan, who are close to a settlement with the Government over a tax-avoidance scheme, told the Financial Times:
Our employee trust has always been transparent ... and its independent trustee has consistently paid taxes in accordance with UK tax law.
JPMorgan are close to a £500 million settlement with the Government over a tax-avoidance scheme for bonuses, according to the Financial Times.
The investment bank is reportedly winding up a Jersey-based trust and has asked more than 2,000 current and former staff to contribute to the settlement.
The news comes with corporations' tax affairs facing increased scrutiny, after Starbucks this week responded to public anger by volunteering to pay millions of pounds to the Treasury.
Corporation tax is not a voluntary tax and Parliament sets out the rules and rates for businesses to follow. The public expects businesses to pay their fair share and HMRC will challenge, through the courts if necessary, any structures or tax payments that do not comply with the UK tax law.
The campaign organisation UK Uncut says that planned protests outside 40 Starbucks stores will take place this weekend, despite the organisation offering to pay £10 million pounds in corporation tax.
Spokeswoman Hannah Pearce said that offering to pay some tax "if and when it suits" did not stop the company being a tax avoider.
"Today's announcement is just a desperate attempt to deflect public pressure" she continued.
"There is no money yet, and hollow promises on press releases don't fund women's refuges or child benefits."