A typical Walmart employee receives $2000 per year in government assistance. The government is essentially subsidizing Walmart's low wages this way. Such low-wage companies should be charged a tax penalty so that they pay this cost.
An employee payed double the minimum wage would incur no penalty. For employees paid less, their employer would be taxed a percentage of the difference between their wage and double the minimum for each hour worked.
Either wages would rise or the government would be able to afford all this public assistance, probably some of both. Poor workers with bigger paychecks would suddenly find themselves able to buy what they've wanted for years, creating an explosion of economic activity and jobs.