** Shares in Brazilian waste management company Ambipar AMBP3.SA plunge more than 50% in midday trading on Friday, heading for its fourth-straight session of losses

** Ambipar announced last week it had secured a preliminary court injunction, temporarily preventing the accelerated maturity of its debt

** The court ruling comes amid a dispute with Deutsche Bank DBKGn.DE, which had demanded additional collateral for loans extended to the company

** Following the announcement, analysts at UBS warned that "the acceleration of one creditor could trigger a cascade across all contracts, pushing Ambipar into technical default and halting operations"

** Ambipar has tapped BR Partners as financial adviser, with a source telling Reuters Ambipar is looking to renegotiate outstanding debt to avoid bankruptcy proceedings

** Ambipar's shares are down 56.4% in the session to about 1.2 reais ($0.23) each, while Brazil's benchmark stock index Bovespa .BVSP gains 0.2%

** Ambipar's shares fell nearly 90% in the last four sessions

($1 = 5.3385 reais)

(Reporting by Isabel Teles and Paula Arend Laier; Editing by Kylie Madry)

((Isabel.Teles@thomsonreuters.com;))