The civils specialist has been suspended by the Chartered Institute of Credit Management who run the code which promises to pay 95% of all supplier invoices within 60 days.
F M Conway is now working with the institute on an action plan to improve its performance.
Demolition specialist Rhodar has also been suspended and is working on speeding up payments.
A raft of contractors have also been re-instated to the code since the last round of suspensions in November.
The reformed contractors are Balfour Beatty, Engie Services, Ferrovial Agroman (UK), John Sisk, Kier Construction, Kier Infrastructure, Galliford Try, Laing O’Rourke and Persimmon.
The CICM’s Chief Executive Philip King, said: “We will continue to challenge signatories to the Code if the obligatory Payment Practice Reporting data suggests that their practices are not compliant.
“We are encouraged by those who have already submitted action plans to achieve future compliance, and we are working closely with those businesses to support a better payment culture.”