Investing in American Workers Act This bill allows a business-related tax credit for employers who increase worker training expenditures. The credit is equal to 20% of the excess of (1) the qualified training expenditures for the taxable year, over (2) the average of the adjusted qualified training expenditures for the three previous taxable years. If the employer had no qualified training expenditures in any one of the three previous years, the credit is equal to 10% of the adjusted qualified training expenditures for the year. The credit applies to expenditures for the training of non-highly compensated employees (annual compensation does not exceed $82,000). The training must result in the attainment of a recognized postsecondary credential and be provided through an apprenticeship program; a program of training services that is included on a list of eligible training providers that states are required to maintain under the Workforce Innovation and Opportunity Act; a program that is conducted by an area career and technical education school, a community college, or a labor organization; or a program that is sponsored and administered by an employer, industry trade association, industry or sector partnership, or labor organization. Certain small businesses and tax-exempt organizations may apply the credit against payroll taxes, subject to specified limits and requirements. Eligible small businesses may also apply the credit against the alternative minimum tax.