US operator Sprint could pull the plug on its deal with LightSquared as early as next week, according to sources at Bloomberg.

Sources say that Sprint will not extend a 15 March deadline for the proposed 4G wholesale operator to secure regulatory conditions – after already pushing back the deadline a number of times. Neither firm was prepared to comment.

Sprint and LightSquared struck an 11-year deal to share network expansion costs and equipment last summer. Sprint was to receive US$9 billion in payments and an additional US$4.5 billion in “service credits” to help build out and operate LightSquared’s network.

According to the report, Sprint has received US$310 million to date and said in a filing last month that it would return as much as $74 million if the agreement was terminated after the 15 March deadline. If LightSquared’s lenders approve changes to the agreement, Sprint’s right to terminate will be deferred until 25 June, according to the filing.

The withdrawal of Sprint from the deal would land a potentially fatal blow to LightSquared, which is being bankrolled by Phillip Falcone’s Harbinger Capital hedge fund. The venture is already facing a cash-flow crisis and last month US regulators said it would block the planned network due to GPS interference concerns. It is also currently looking for a new CEO after the recent resignation of Sanjiv Ahuja.