The lawsuits were filed separately between 1 September and 14 September by two pension funds and two individuals, all of them apparently relatively minor shareholders in Tesla.

Tesla flagged up the lawsuits in a regulatory filing, and said they are all “without merit”.

The lawsuits will be consolidated, and an initial court hearing has been set for 18 October. If the judge were to grant an injunction to give the lawsuits more time to play out, it could push the acquisition into 2017.

That would be a blow to SolarCity, whose future is seen as more reliant than Tesla’s on the acquisition going through – and whose shares have been sinking in recent weeks as investors bet the deal will fall apart.

One SolarCity board member has reportedly said the company will look to find another strategic partner in the event Tesla’s acquisition does not work out.

Tesla and SolarCity intend for the acquisition to be completed by the end of this year.

While injunctions on M&A deals are granted to shareholders only relatively rarely, there are special circumstances at play in the proposed Tesla-SolarCity tie-up, not least the family connections between Elon Musk (chairman of both companies and chief executive of Tesla) and his cousins Lyndon and Peter Rive (chief executive and chief technical officer of SolarCity) – and the fact that Musk is the largest shareholder of both companies.

Both Tesla and SolarCity have taken steps to defuse any conflicts of interest, including Musk recusing himself from voting on the deal. The lawsuits, however, allege these steps have been insufficient.

Despite the growing number of challenges facing the deal, many analysts still expect it to go through. One reason for that is that there is a heavy overlap in the investor base in both companies.

Many such investors are apparently convinced by Musk’s grand vision for a future transportation economy underpinned by clean solar power, and would also be damaged by the likely collapse in SolarCity's stock price were the deal to fall through.

According to Bloomberg, seven of the top 10 owners of Tesla Motors also own stakes in Tesla, including Fidelity Investments and BlackRock.