By Mehreen Zahra-Malik
ISLAMABAD (Reuters) - Pakistani lawmakers voted for new senators in parliament's upper house on Thursday in an election that could strengthen Prime Minister Nawaz Sharif's grip on power and increase his ability to pass important legislation.
The main opposition party, the Pakistan People's Party (PPP), currently holds a majority in the Senate.
But projections by analysts indicate that after Thursday's vote, Sharif's ruling Pakistan Muslim League is expected to win almost equal representation in the upper house.
Under the constitution, a bill cannot become law unless it is passed by both upper and lower houses of parliament.
Sharif, whose party holds a majority in the lower house of parliament, has his hands full with problems ranging from chronic power shortages, a near-failed economy, a Taliban insurgency and building relations with the United States and arch-rival India.
Toppled in a 1999 coup, jailed and later exiled, Sharif made a triumphant election comeback in May 2013, becoming prime minister for a third time and winning enough seats so he did not need to form a coalition with other major parties to push through badly needed reforms.
There are 132 candidates in the running for 48 Senate seats on Thursday.
Members of both houses of parliament vote and results are expected later in the day. The newly elected senators will take oath and elect a chairman on March 12.
(Writing By Mehreen Zahra-Malik; Editing by Robert Birsel)