US President Donald Trump has signed an executive order to end collective bargaining with federal unions in some agencies that have "national security missions", the White House said.The order would apply to unions in agencies such as the National Aeronautics and Space Administration (Nasa), the Patent and Trademark Office, the National Weather Service and others, the White House said in a statement.Trump also signed a presidential memorandum aimed at preventing federal grant money from going toward political lobbying, the White House said.The memo directs Attorney-General Pam Bondi to investigate whether funds from federal grants "are being illegally used to support lobbying activities and to take appropriate enforcement action", according to a White House fact sheet.