Improving Access to Retirement Savings Act This bill allows employers who establish a tax-exempt 403(b) pension plan to participate in a multiple employer plan (MEP) and to take the small employer pension plan start-up tax credit for their first three years of participation in a MEP. The bill also establishes a safe harbor to allow certain pension plans to correct errors in administering automatic enrollment and escalation features for plans enrolling in a MEP, if such errors are corrected within a specified time period in a manner favorable to plan participants. It also permits employers that amend a stock bonus, pension, profit sharing, or annuity plan for a previous plan year to increase benefits accruals to elect to treat such amendment as having been adopted at the end of the current plan year.