In a letter to U.S. District Judge Sidney Stein in Manhattan, prosecutors asked that the May 6 trial date be pushed back to July or August, though they still oppose granting the Menendezes' requests to be tried separately.

Prosecutors said the government "takes seriously the unexpected medical development," and that an adjournment would let the Democratic senator focus on his wife's health. They opposed Nadine Menendez's request for an indefinite adjournment.

Lawyers for the senator and his wife did not immediately respond to requests for comment.

Nadine Menendez has not disclosed her medical condition, but her lawyers said it would require surgery within four to six weeks and potentially significant follow-up treatment.

They also said that she would not be in a "physical or psychological condition" to participate in the currently scheduled trial, which is expected to last six weeks.

The couple and two other defendants have been charged in a wide-ranging bribery conspiracy, and have pleaded not guilty.

Prosecutors accused the senator of accepting cash, gold bars and a luxury car to wield his influence at home and on behalf of Egypt's and Qatar's governments. They also charged the Menendezes with obstruction of justice.

Senator Menendez was forced to give up his chairmanship of the Senate Foreign Relations Committee following his arrest last September, and has resisted many calls to resign.

He is up for re-election in November but chose not to run in New Jersey's Democratic primary, and instead hopes to run as an independent if he is exonerated.

Democrats and independents who caucus with them hold a 51-49 Senate majority. Several seats held by Democrats or independents may be closely contested in November's election, and a seat in West Virginia is widely expected to turn Republican.