The consumer protection department of the Justice Ministry has opened an investigation of cellphone operators TIM Participacoes (TSU) and Claro, the local cellphone unit of America Movil (AMX), as part of a clamp down on poor customer service and lax call centers, the Ministry said in a statement Thursday.

Since December, Brazilian companies have had to adapt to new tight rules governing customer services and call centers in particular.

According to the Justice Ministry, TIM, a subsidiary of Telecom Italia S.p.A. (TI) and Claro are among the 204 companies being investigated since the new consumer service law came into force. Among the subjects of complaints are telephone companies, banks and airlines.

The two companies will be notified and asked to present their defense.

Spain's Telefonica (TEF), which runs fixed-line and Internet broadband services in Sao Paulo state via Telecomunicacoes de Sao Paulo (TSP) has also received criticism for poor customer service.

Earlier Thursday, public prosecutors announced that they had brought a 1 billion Brazilian real ($437 million) suit against Telefonica for damages related to poor service over the past five years.

-By Alastair Stewart, Dow Jones Newswires; 5511 2847-4520; alastair.stewart@dowjones.com