Sept 22 (Reuters) - Electric vehicle company Workhorse Group (WKHS.O) said on Wednesday it would suspend the deliveries of its flagship C-1000 electric van, saying more tests and modifications were needed to ensure it complies with regulatory standards. Workhorse"s shares plunged about 14% to touch a more than one-year low of $7.05 as the company also said it would recall the 41 vans it had already delivered, even though it had not received reports of safety issues from customers. The suspension and recall adds to the Workhorse"s woes, as it is said to be under a probe by the U.S. Securities and Exchange Commission, according to a letter from the regulator published by a short seller this month. read more The Ohio-based firm said its new leadership team had concluded that modifications were necessary to certify the C-1000 vehicles under Federal Motor Vehicle Safety Standards (FMVSS). The company expects to complete testing of the C-1000 in the fourth quarter. The van has a range of 100 miles and is powered by a 70 kilowatt hour battery. Workhorse added that it had informed the National Highway Traffic Safety Administration about the need for modifications and said its previous statements related to van"s compliance with agency"s standards cannot be relied upon. Last week, the electric vehicle maker had voluntarily dismissed its legal challenge against a U.S. Postal Service (USPS) move to award a multibillion-dollar contract to Oshkosh (OSK.N) for delivery vehicles.