Blue slipping is a House rule involving the act of sending a bill back to the Senate because it violates House prerogatives—the resolution is printed on blue paper, hence the name.
The decision to return a bill to the Senate is determined by a majority vote in the House of Representatives. This may be the vehicle by which convervatives in the House rid themselves of that nasty immigration bill: S.2611
Certain Senators are aware of this potential snafu but are hoping to salvage the present Senate bill by hijacking a tax bill which has already passed the House. Technically the Senate could use the tax portion of that bill, strip out the rest of the language, replace it with the contents of S. 2611 and send ot back to the House for approval.
Voila! The Senate bill would still be a tax bill but not one which originated in the Senate and as such, perfectly constitutional.
Sneaky and under-handed but constitutional.
So far the Republican leadership has been unable to garner unanimous consent to pursue this plan.
Additionally, the highly anticipated joint conference between House and Senate representatives has yet to be scheduled.