(Adds details on bonding, bill backlog, background on budget impasse and on status in Senate)
CHICAGO, July 3 (Reuters) - The Illinois House of Representatives on Monday passed a bill for the final piece of the state's fiscal 2018 budget that includes authorization for $6 billion of bonds to pay down a $15 billion bill pile.
The budget implementation bill was sent to the Senate on a 72-36 vote. The House on Sunday passed appropriation and revenue bills that require concurrence votes in the Senate.
In passing the budget implementation bill, a dozen House Republicans joined majority Democrats to reach a 73-vote threshold that could withstand a possible veto by the governor if the measure passes the Senate. Republican Governor Bruce Rauner has already said he will veto the revenue bill that includes a big income tax rate hike.
The Senate was in session on Monday, but it was not clear when the chamber would take up the budget measures.
A stalemate between the state's Republican governor and Democrats who control the legislature has left the nation's fifth-largest state without a complete budget for two-straight fiscal years. While fiscal 2018 began on Saturday, lawmakers have been scrambling to piece together a spending and revenue plan to avoid Illinois becoming the first-ever U.S. state to be rated junk.
Illinois already pays the biggest penalty among states in the U.S. municipal bond market, and a junk rating would make selling new debt difficult and expensive.
In addition to the up to $6 billion of general obligation bonds, the House-passed bill allows money to be borrowed from Illinois' myriad of funds allocated for specific purposes.
State Representative Greg Harris, the House Democrats' budget point person, said enough money has been identified only to cover debt service on $3 billion of bonds and that the rest of the debt could be issued once additional revenue is available.
He added the legislation is aimed at shrinking Illinois' unpaid bill pile, which ballooned to about $15 billion due to the impasse, by $8 billion. (Editing by David Gregorio and Matthew Lewis)