"In general, after a session of Congress ends, the Congressional Budget Office [CBO] is required to issue a report that provides estimates of the limits (often called caps) on discretionary budget authority that are in effect for each fiscal year through 2021. As part of that requirement, CBO also must report whether, according to its estimates, enacted legislation for the current fiscal year has exceeded those caps. If so, a sequestration (that is, a cancellation of budgetary resources) would be required. [...] In CBO's estimation, a sequestration will not be required for 2017. However, the authority to determine whether a sequestration is required and, if so, exactly how to make the necessary cuts in budget authority rests with the Administration's Office of Management and Budget (OMB). Those determinations are based on OMB's own estimates of federal spending."
Congressional Budget Office: http://www.cbo.gov/