Laravel Many to Many Relationship Users on Shift - php

Question

I'm trying to get the users that are on today's shift. I have a many to many relationship between the User and Shift model with a pivot table called user_shifts.
My User model:
/**
* Get the users shifts
*/
public function shift()
{
return $this->belongsToMany('App\Shift', 'user_shifts', 'user_id', 'shift_id');
}
My Shift model
/**
* The shift can have many users
*/
public function users()
{
return $this->belongsToMany('App\User', 'user_shifts', 'shift_id', 'user_id')->withPivot('start_time', 'end_time');;
}
In my controller I thought I could do something like:
$shift = Shift::all()->where('date', date('Y-m-d'));
$users = User::all()->where('shift_id', $shift);
return $users;
But that is returning null. Any help would be appreciated!
If it matters my db schema is:
Schema::create('shifts', function (Blueprint $table) {
$table->increments('id');
$table->date('date');
$table->boolean('weekend');
});
Schema::create('user_shifts', function (Blueprint $table) {
$table->increments('id');
$table->integer('shift_id');
$table->integer('user_id');
$table->time('start_time');
$table->time('end_time');
});
Schema::create('users', function (Blueprint $table) {
$table->increments('id');
$table->string('fname');
$table->string('lname');
$table->string('email')->unique();
$table->string('password', 60);
$table->rememberToken();
$table->timestamps();
});