* TIM, other mobile operators face crackdown on poor service
* Regulator needs at least two weeks to vet investment plans
RIO DE JANEIRO, July 19 (Reuters) - Telecom Italia's Brazil unit said late on Thursday that it will challenge in court a penalty by the country's telecommunications regulator that suspended its sale of mobile phone plans in 19 states due to complaints over service.
The penalty is part of a drive by Brazil's regulator, known as Anatel, to push the country's mobile operators to improve coverage and customer service as consumer complaints soar.
TIM Participações said it would file a court challenge to the sales halt on Friday, stating that the penalty was "excessive and creates an imbalance in competitiveness of the market".
Anatel on Wednesday also ordered two other mobile operators to halt sales in various states, although TIM received the stiffest penalty.
The suspensions are to remain in place for each company until they present an investment plan to show how they will improve service. Once a plan is presented, it will take the regulator at least two weeks to evaluate whether it is sufficient for a lifting of the ban, an Anatel official told Reuters on Thursday.
The other two operators facing bans are Grupo Oi and Claro, a unit of Mexican tycoon Carlos Slim's America Movil .
The severity of TIM's penalty caused shares in Telecom Italia to tumble at the Milan stock exchange on Thursday. Trading in the shares was halted at one point as the stock fell by 8 percent.