Due to take place tomorrow afternoon, the demonstration comes ahead of the union presenting its Hopelessly Addicted to Low Pay submission to the Great London Authority (GLA) at the nearby City Hall.
The document is calling for the hospitality industry to pay the London Living Wage (LLW) of £8.55 per hour.
Unite said that there were currently no hospitality employers in London that independently endorsed and paid their employees the LLW, recognising that some food service companies paid it to their staff in contracts where the client insisted on it.
"Many of our members are forced to live on little more than the national minimum wage (currently £6.19p an hour)," states the submission. "Many report suffering pay freezes, pay cuts and constant attacks on their terms and conditions of employment."
Unite said that, with the 4.2% growth in the number of overseas visitors to the capital (to 3.4 million) during the first quarter of 2013, compared with the same period last year, it was "entirely realistic and feasible" for the LLW to become the norm within the hospitality sector by 2020.
Unite regional officer Dave Turnbull said: "We believe that the Living Wage would have a positive impact on the problems of high staff turnover and skill shortages that have plagued the sector for decades. It should not be forgotten that tourism/hospitality is the UK's fourth-biggest industry.
"The adoption of the Living Wage would enhance London's reputation as a world-class tourist destination fit for the 21st century."
Despite Unite's assertion that there are no hospitality companies endorsing the LLW, InterContinental Hotels Group (IHG) became the first company to announce its support for the payment last year, although it is yet to pay it in full.
Stephen McCall, managing director of IHG, UK & Ireland, said: "We've made a commitment to become a London Living Wage Employer in all the London hotels we manage over the next five years."
However, the British Hospitality Association said that, with the potential for the hospitality industry to create more than 200,000 jobs in the UK by the end of 2015, now was not the right time to increase wages.
"At a time when our priority is getting more people into work, any increase in staff costs would be a hurdle too high," a spokesperson said. "Fifteen per cent of hospitality employees are under 20 - and young, unskilled people are facing some of the biggest challenges on the jobs market at the moment. A general switch to the Living Wage would make it impossible for the industry to expand and create the jobs needed."