WASHINGTON (AP) — Treasury Secretary Timothy Geithner says the government has begun borrowing from the federal employee pension fund to keep operating without surpassing its debt limit.

Geithner says in a letter to congressional leaders that the move will free up $156 billion in borrowing authority while Congress debates increasing the $16.4 trillion debt limit.

The government reached its borrowing limit on Dec. 31, but began using bookkeeping maneuvers to keep from surpassing it. Geithner has told congressional leaders that Treasury expects to exhaust those measures by mid-February to early March.