United States lawmakers have less than seven days until authorisation for the Government to spend money runs out.
If a deal cannot be reached between Congressional Democrats and Republicans, a government shutdown could be forced.
The Republicans are demanding that President Barack Obama's healthcare plan be de-funded, despite their challenge to it being defeated in the US Supreme Court.
The Democrats have vowed not to pass any funding bill which de-funds Obamacare, which may cause a deadlock.
Shares on Wall Street fell for the fourth straight session as investors grow more cautious.
A BBC correspondent says the next looming concern for investors will be whether the US Government will raise its debt ceiling. There are concerns about what could happen to the US economy if the debt ceiling is not increased.
The last time the US Government shut down was in the Clinton era of the mid 1990s, costing the country more than $1 billion.