Pioneer Municipal High Income Fund (MHI) Form 4 PIONEER MUNICIPAL HIGH INCOME TRUST / FARGO & COMPANY/MN WELLS ownership change

                                                                    EXHIBIT 99.1

                               JOINT FILING AGREEMENT

    Pursuant to and in accordance with the Securities Exchange Act of 1934, as
amended (the "Exchange Act"), and the rules and regulations thereunder, each
party hereto hereby agrees to the joint filing, on behalf of each of them, of
any filing required by such party under Section 13 or Section 16 of the Exchange
Act or any rule or regulation thereunder (including any amendment, restatement,
supplement, and/or exhibit thereto) with the Securities and Exchange Commission
(and, if such security is registered on a national securities exchange, also
with the exchange), and further agrees to the filing, furnishing, and/or
incorporation by reference of this agreement as an exhibit thereto. This
agreement shall remain in full force and effect until revoked by any party
hereto in a signed writing provided to each other party hereto, and then only
with respect to such revoking party.

    IN WITNESS WHEREOF, each party hereto, being duly authorized, has caused
this agreement to be executed and effective as of the date set forth below.

Date:  February 18, 2021      WELLS FARGO & COMPANY

                              By: /s/ Patricia Arce
                                  ------------------------------
                                  Name: Patricia Arce
                                  Title: Designated Signer


                              WELLS FARGO MUNICIPAL CAPITAL STRATEGIES, LLC

                              By: /s/ Alejandro Piekarewicz
                                  ------------------------------
                                  Name: Alejandro Piekarewicz
                                  Title: Vice President