Making Pipelines Accountable to Consumers and Taxpayers Act or the MPACT Act This bill revises the authority of the Federal Energy Regulatory Commission (FERC) regarding rates and charges in connection with the transportation or sale of natural gas. Specifically, the bill provides FERC the authority to set a refund effective date and order a natural gas company to provide refunds when a rate or charge is unjust, unreasonable, unduly discriminatory, or preferential; and requires FERC to conduct a study on the impact of such authority on the cost of capital paid by natural gas companies and the average time it takes to resolve proceedings related to rate changes.