Opposition parties on Thursday criticised legislation passed by the National Assembly, which gives the military a formal role in politics.
The National Assembly on Wednesday approved the government bill to set up a National Security Council in which military top brass will sit with civilian leaders to take decisions on issues of national importance.
The bill will be sent to the Senate, for debate and approval on Friday.
Opposition MNAs criticised the bill and said they would try to block it in the Senate, where the government also enjoys the simple majority required to pass the legislation.
"I regard it to be a disservice to Pakistan and a violation of constitution," Senator Khurshid Ahmed, vice president of Jamaat-e-Islami, told AFP.
"It is an effort to institutionalise the role of the army in politics and it is against the national interest and not in the interest of the army who must be above board and not become controversial by being involved in politics," Ahmed said.
"In Senate we will fight inch by inch and prevent the passage of this bill."
Since independence from Britain in 1947, Pakistan has had alternate periods of military and civilian rule.
Pakistan Muslim League (Nawaz) said the military would overshadow the elected prime minister and his cabinet.
"PML-N is of the opinion that it (National Security Council) will cripple the powers of prime minister and his cabinet," spokesman Siddiqul Farooq told AFP. Senator Raza Rabbani of Pakistan Peoples Party said the creation of the council "amounts to the militarisation of the constitution of 1973."
A ruling party spokesman insisted the 13-member council was necessary to create harmony between the civilian and military leadership on important issues and strengthen the democratic process.
"It will in fact act as a safety valve and will strengthen the democratic process in the country," Pakistan Muslim League spokesman Senator Tariq Azeem Khan told AFP.
The council will be a consultative body and comprise nine elected civilian politicians and four military members, Khan said.