Measures to criminalise cyber-flashing and give a right to appeal against the removal of social media posts are among changes the government has proposed to its Online Harms Bill.
The bill, which also seeks to tackle access to harmful material online, has been introduced to parliament.
It would give regulator Ofcom the power to fine firms or block access to sites that fail to comply with the new rules.
But Labour says delays to the bill mean disinformation in the UK has increased.
The bill - originally announced in 2019 - covers a wide array of topics relating to harmful material online.
Big social media companies will be required to assess risks of the types of legal harms against adults which could arise on their services, and will have to set out how they will deal with them - and enforce these terms consistently.
Definitions of these legal harms will be set out in additional legislation, but potential examples could include material promoting self-harm, eating disorders or harassment.
Some of the additional aspects of the bill announced as it was introduced to Parliament include:
- Criminalising the sending of unsolicited sexual images to people using social media, known as cyber-flashing
- Giving people the right to appeal if they feel their social media posts were removed unfairly
- Preventing online scams, such as paid-for fraudulent adverts, investment fraud and romance scammers
- Requiring pornography websites to verify their users' ages
Culture Secretary Nadine Dorries said the bill meant technology companies would not be left to "check their own homework".
"Tech firms haven't been held to account when harm, abuse and criminal behaviour have run riot on their platform," she said.
The bill will give new powers to Ofcom, which will be able to request information from companies, and executives who do not comply could face up to two years in prison within two months of the bill becoming law.
Senior managers would also be criminally liable if they destroyed evidence, did not attend an Ofcom interview, provided false information, or otherwise obstructed the regulator from entering offices.
Any firm breaching the rules would face a fine of up to 10% of its turnover, while non-compliant websites could be blocked entirely.
Children's charity Barnardo's welcomed the announcement sites showing pornographic material would have to check the ages of users.
"We know from our work with children and young people across the UK that exposure to pornography can have a harmful impact on their mental health and understanding of what makes a healthy relationship," chief executive Lynn Perry said.
And a City of London Police Authority Board spokesperson said included paid-for advertising in the legislation was "a major step forward in the fight to reduce online crime, and helps cement the benefits of including fraud as a priority harm".
But shadow culture secretary Lucy Powell likened said the bill's delays had "allowed the Russian regime's disinformation to spread like wildfire online".
She added: "Other groups have watched and learned their tactics, with Covid conspiracy theories undermining public health and climate deniers putting our future at risk."
The legislation has taken some time to reach the stage where a bill is now to be laid before Parliament.
An Online Harms White Paper was first introduced in April 2019 by the Conservative government - then led by Theresa May.
At the time, privacy organisations such as the Open Rights Group warned that the bill could threaten freedom of expression.
Commenting on the length of the delay, Jim Killock, Open Rights Group executive director said: "The fact that the bill keeps changing its content after four years of debate should tell everyone that it is a mess, and likely to be a bitter disappointment in practice."