Labour MPs have been warned they must not put down any amendments on government bills and must resolve disagreements privately with ministers, in a crackdown on dissent in parliament. In a private message, seen by the Guardian, Labour whips told MPs they could no longer act as if they were in opposition and said amendments suggested a lack of trust in the government. The message said MPs should be speaking with “one voice” in public. There are a number of bills where there is pressure for the government to go further, such as the GB Energy bill and the employment rights bill. But the whip warned it was “not very helpful” for MPs to be putting amendments against their own government, adding: “We are not in opposition any more.” They said ministers would be happy to have discussions and “reassure them that their concerns are taken into account”, but amendments “make it look like we don’t trust our own government to deliver”. The whips suggested MPs could seek reassurance on issues they were passionate about in different ways during the progress of bills such as in speeches, on social media or in private with ministers. “We should be supporting Labour legislation wholeheartedly and working with our ministers so we have one voice. We are a team – it’s your government and your bill too now,” the message said. The autumn will bring a slew of major legislation, as well as the budget on 30 October. In addition to the employment rights bill and the establishment of Great British Energy, MPs will vote on renters’ rights, planning reform and the terrorism protection bill known as Martyn’s law. The message is the latest warning from Labour whips, who are also said to have made clear that any MPs who abstained on the winter fuel allowance vote would be given no help to obtain coveted places on select committees. Rebels who voted with the SNP amendment to the king’s speech on the two-child benefit cap have been stripped of the Labour whip for six months. MPs were also told in the aftermath of the winter fuel vote that they were not allowed to discuss parliamentary discipline with journalists and must only raise concerns privately with ministers. Labour MPs are in a frenzied jostle for places on select committees, elections for which will be held next week between Monday to Wednesday. New MPs and those who missed out on ministerial appointments have been told there is fierce competition for places on the most prestigious committees, such as those for the Treasury, foreign affairs, home affairs and health. Previously, places on select committees were solely decided by party whips, but changes after the 2010 election removed that power and introduced the election of select committee members. The theory was that government MPs could be critical and scrutinise properly as part of committee without being concerned about being removed by disgruntled whips. But in practice, whips are able to influence which MPs apply for which committees, spotting spaces on less popular ones and moving them from those which are oversubscribed. A Labour spokesperson said: “We do not comment on whipping.”